McLaren's Lewis Hamilton set the pace in Hungarian Grand Prix practice from Lotus's Kimi Raikkonen.
He headed both sessions. Team-mate Jenson Button was second in the first and eighth in the second, which was disrupted by a rain shower.
Hamilton ended the day 0.185 seconds quicker than Raikkonen, with Williams's Bruno Senna a surprise third.
The Ferrari drivers Felipe Massa and Fernando Alonso were fourth and fifth, and Red Bull's Sebastian Vettel eighth.
"It's been a real positive day for me, I'm very happy," said Hamilton.
"We're on the right path but we've still got work to do and we know the Red Bull looks very quick, so does the Lotus and obviously the Ferrari as well.
"So we are by no means feeling comfortable. We're going to keep pushing."
Red Bull, who have dominated in the dry at the Hungaroring in the last two seasons, were surprisingly off the pace in the first session, although they looked more competitive in the second.
Vettel was 0.829 secs behind Hamilton in the second session, while team-mate Mark Webber was 14th fastest in the afternoon, although neither ran the faster 'soft' tyres before it rained.
Webber was 13th in the morning, when Vettel was 15th.
Speculation will centre on whether this apparent comparative lack of pace is related to a
rule change focused on Red Bull and the engine settings they were running at the German Grand Prix last weekend.
The second session was interrupted by a rain shower about halfway through, but most of the leading runners managed to get out to do their lower-fuel runs on the 'soft' tyre before it hit.
"Some drivers did not get the best out of the 'soft' tyres, such as Button," said BBC F1 technical analyst Gary Anderson. "Hamilton, Raikkonen and Senna all benefited from the cloud cover before the rain started.
"The Renault engine-setting situation will affect the mapping for the wet as well as the dry, but I'm sure Red Bull will be a factor [in the race]."
Force India's Paul di Resta was seventh fastest, with Lotus's Romain Grosjean ninth, ahead of the Mercedes of Michael Schumacher and Nico Rosberg.
Schumacher went out on wet tyres after the rain but locked his brakes and crashed into the tyre barriers at the downhill Turn 12.
It was the second time in a week that the veteran German had crashed in a wet second practice session.
"I just locked up and run out of road," The Mercedes driver said. "By hitting the tyres, I lost the front wing, but other than that, nothing is damaged on the car, I believe.
"It was the kind of incident that happens when suddenly a shower hits the dry track. The car felt OK until then."
The rain meant that the teams did not have a chance to do their usual race-simulation runs on the softer tyre.
In the first session, there was another impressive performance from Williams reserve driver Valtteri Bottas, standing in for race driver Bruno Senna in this sesson as normal.
He finished the session ninth fastest, behind Mercedes' Nico Rosberg, Ferrari's Felipe Massa and Lotus driver Kimi Raikkonen.
Bottas was 0.148 secs quicker than team-mate Pastor Maldonado - and 15 minutes before the end of the session he had been seventh quickest, nearly half a second ahead of the Venezuelan.
In the first session, Hamilton was 0.101 secs quicker than Button, with Alonso third and a further 0.475 secs behind.
Hungarian Grand Prix 2012, day two
- Saturday, 28 July: Third practice 09:55 BST; BBC Sport website live text and audio commentary and BBC Radio 5 live sports extra. Qualifying 12:55 BST; BBC Sport website and BBC Radio 5 live sports extra & highlights on BBC Two at 17:00 BST.
Hungarian Grand Prix 2012, day three
- Sunday, 29 July: Race 12:45 BST; BBC Sport website live text and audio commentary and BBC Radio 5 live sports extra & Race highlights 19:00 BST BBC One/BBC HD/online.