World champions Renault and rising stars Red Bull both gave their new Formula One cars their first outing in testing at Jerez in Spain on Tuesday.
Fisichella put the new Renault through its paces in Jerez
Giancarlo Fisichella put the first miles on Renault's new R26, which bore a striking resemblance to last year's double-title-winning R25.
And David Coulthard drove Red Bull's new R3B, which featured a much higher, flatter nose than its predecessor.
"My first impression is the car has a lot of potential," Fisichella said.
"We had a very promising first day with the R26. I felt comfortable straight away, and the programme was to do as much mileage as possible, while proceeding with all the checks you have to do on a new car.
"This wasn't a day to go for lap-times, and it was hard to get the tyres working in the cold temperatures.
"The V8 engine felt very good, similar to our predictions and it was reliable for the first run. My first impression is that this is a car with a lot of potential."
Fisichella was 0.6secs slower than team-mate Fernando Alonso, the world champion, who was driving a modified version of last year's Renault.
That is an encouraging sign for the first day's testing of a new car, which was also giving the team's new V8 engine its debut run.
Bob Bell, Renault's chassis technical director, said: "As with any new car, there were some minor issues to resolve, but we did not encounter any major problems and gradually began completing some longer runs.
"The purpose of the day was very simple: to put miles on the new package.
Coulthard's laps in the new Red Bull were restricted by a failure
"From what Giancarlo could tell, the car is responding in the same way as the R25, which is in line with our predictions, and our objectives.
"The engine's first track test went very smoothly, and the V8 was behaving normally as it completed nearly 200km. All in all, it was a pleasing opening day of testing with the new car."
Michael Schumacher's 2005 Ferrari set the fastest time of the day.
The seven-time champion was driving a car fitted with Ferrari's new 2.4-litre V8 engine - a format demanded by a change in rules outlawing the three-litre V10s which have been used since 1995.
The German set a fastest time of one minute 18.020 seconds as testing resumed after a Christmas break - more than a second faster than Toyota test driver Ricardo Zonta in the Japanese team's new TF106 car.
Zonta's team-mate Ralf Schumacher was third fastest, ahead of Alonso and Ferrari test driver Luca Badoer.
Coulthard was slowest of all after being hit by a mechanical problem early in the day that left him stranded out on the track.
Red Bull technical director Mark Smith said: "It was something of a scrappy day.
"Our priority had been to see if we had solved the cooling problem we encountered at Silverstone and the short answer is that we have not.
"However, it did not prevent us from running.
"We went for the short-term fix of additional holes in the bodywork, and we were able to begin work on seeing how the new car reacts to set-up changes, while also embarking on a tyre test programme that takes into account the fact we will once again be able to change tyres during the races this season."