Ferrari are favourites for Sunday's Turkish Grand Prix after dominating practice on Friday.
Felipe Massa set the pace in first practice and Kimi Raikkonen in the second as they outpaced rivals McLaren.
The Finn's pace was particularly impressive in the afternoon - he missed the morning with a gearbox problem.
McLaren's Lewis Hamilton was slower than team-mate Heikki Kovalainen for much of the day but set second fastest time at the end of the second session.
"We focused on tyre evaluation and set-up work and so far things are not looking too bad," said Hamilton.
"This circuit is constantly evolving which is challenging but also enjoyable.
"In the first session I stayed on the same set of tyres throughout and experienced no problems."
Hamilton might even have been fastest of all in the afternoon had it not been for a slide in the middle of the demanding Turn Eight, 100mph double left-hander.
"In my last run of the day I put on a new set of tyres but had a small moment which cost me some time," he added.
"Overall I'm pleased with our initial pace and consistency."
In the later stages of the second session Raikkonen appeared not to be concerned about trying to improve his fastest time of one minute 27.543 seconds, which was set at the end of his first run.
Massa set the fastest time of the day - 1:27.323 - in the first session, which was run in warmer, quicker conditions.
That was 0.133secs ahead of Kovalainen, who was back in the car for the first time since being concussed in a high-speed accident at the Spanish Grand Prix.
The Finn was slightly less than 0.3secs ahead of Hamilton in the first session and a similar margin behind in the afternoon.
"It was nice to get back in the car again and everything was fine. I was on the pace immediately and was able to set some consistent lap times," he said.
Until his late turn of speed, Hamilton had appeared to be struggling on the difficult and technical Turkish track.
He had a spin in the morning, and was marginally off the pace of his team-mate throughout the first 90 minutes of practice.
Massa, who has won the last two races in Turkey, traded fastest times with Kovalainen throughout the first session, with Hamilton a little way back in third.
"I've had a fantastic race here for the last two years," said Massa.
"Two years ago on this track I enjoyed my first victory in F1, so it is a very special place for me.
"Last year I repeated the victory, so hopefully now I can have a third one. It would be fantastic, and I will push hard for it."
The Brazilian punctuated his first session with a couple of lurid moments - a big opposite lock slide in turn seven, and running off the track in turn eight.
Raikkonen completed only one flying lap in the morning before a gearbox problem consigned him to the pits for the rest of the 90-minute session and to the bottom of the time sheets.
Renault's revival continued following their impressive step forward in Spain, with Fernando Alonso setting fourth fastest time, 0.961secs off Massa's pace.
The double world champion was ninth fastest in the afternoon.
"We still have to make a few more improvements on Saturday, especially with the general balance of the car, but this performance is encouraging for the rest of the weekend," said Alonso.
Red Bull's David Coulthard split the Ferraris and McLarens in the second session with fourth fastest time, while running with less fuel.
The Scot's team-mate Mark Webber missed most of the second session when he crashed his car after running off the track.
Jenson Button's Honda was a striking fifth in the morning, but only 11th in the second session.
His team-mate Rubens Barrichello - celebrating his record-breaking 257th Grand Prix this weekend despite doubt about whether he has yet officially achieved that mark - was not quite on his team-mate's pace.
• Force India driver Giancarlo Fisichella has been handed a three-place grid penalty for ignoring a red light at the exit of the pit lane in the first session.
Times from first practice at the Turkish Grand Prix:
1 Felipe Massa (Brz) Ferrari one minute 27.323 seconds
2 Heikki Kovalainen (Fin) McLaren-Mercedes 1:27.456
3 Lewis Hamilton (GB) McLaren-Mercedes 1:27.752
4 Fernando Alonso (Spa) Renault 1:28.284
5. Jenson Button (GB) Honda 1:28.919
6. Kazuki Nakajima (Jpn) Williams-Toyota 1:29.002
7. Nick Heidfeld (Ger) BMW Sauber 1:29.024
8. Rubens Barrichello (Brz) Honda 1:29.068
9. Nelson Piquet Jr (Brz) Renault 1:29.082
10. Timo Glock (Ger) Toyota 1:29.103
11. Jarno Trulli (Ita) Toyota 1:29.329
12. Robert Kubica (Pol) BMW Sauber 1:29.330
13. Nico Rosberg (Ger) Williams-Toyota 1:29.367
14. Adrian Sutil (Ger) Force India-Ferrari 1:29.756
15. Giancarlo Fisichella (Ita) Force India-Ferrari 1:29.811
16. Mark Webber (Aus) Red Bull-Renault 1:30.088
17. David Coulthard (GB) Red Bull-Renault 1:30.340
18. Sebastien Bourdais (Fra) Toro Rosso-Ferrari 1:30.388
19. Sebastian Vettel (Ger) Toro Rosso-Ferrari 1:30.426
20. Kimi Raikkonen (Fin) Ferrari 1:30.732
Second session:
1 Raikkonen 1:27.543
2 Hamilton 1:27.579
3 Massa 1:27.682
4 Coulthard 1:27.763
5 Kovalainen 1:27.954
6 Kubica 1:28.431
7 Trulli 1:28.619
8. Nakajima 1:28.664
9. Alonso 1:28.681
10. Heidfeld 1:28.817
11. Button 1:28.826
12. Glock 1:28.849
13. Rosberg 1:28.907
14. Fisichella 1:29.008
15. Barrichello 1:29.024
16. Piquet 1:29.212
17. Vettel 1:29.462
18. Bourdais 1:29.630
19. Webber 1:29.633
20. Sutil 1:30.832
Follow live coverage of the Turkish Grand Prix on the BBC Sport website and 5 Live. Qualifying starts at 1200 BST on Saturday, with the race at 1300 BST on Sunday
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