Stage 19: Pornic - Nantes (49km).
All the action from as it happened (all times BST).
With heavy rain and strong winds making for treacherous conditions, Lance Armstrong retains his yellow jersey and extends his lead over Jan Ullrich after the German rider has a nasty fall.
Britain's David Millar takes the stage in a time of 54 minutes 05 seconds with a brilliant time trial performance.
1556: Armstrong crosses the line in a time of 54mins 19secs to take third place in the trial but, more importantly, he retains the yellow jersey and extends his overall lead over Ullrich to one minute 16 seconds.
1553: Ullrich comes home in a time of 54mins 30secs in third place behind both Millar and Hamilton.
1552: Armstrong is taking a safety-first approach to all the corners.
1550: Tyler Hamilton completes the time trial, finishing in second place, nine seconds behind Britain's Millar.
1548: With seven kms to go, Armstrong goes through the same check point just 12 seconds behind Millar. The four-time champion is in control of the race.
1546: At the third time check, the impact of Ullrich's fall becomes clear as he goes through 22 seconds down on Millar.
1545: Coming through the same corner that Ullrich fell on, Armstrong is clearly taking no risks as the information about his rival's fall filters through.
1544: The German looks jumpy and appears to have lost his rhythm as he gets back on his bike. That should be enough to send him into fourth place in the overall standings.
1541: Disaster for Ullrich as he falls off while negotiating a corner. The German was pushing hard but the surface water sends the bike from underneath him. The fall may well have cost him about 15 seconds.
1537: Armstrong goes through the same checkpoint in 35mins 21secs, meaning that Ullrich has taken two seconds out of Armstrong. But with a lead of more than one minute, Armstrong is still in control.
1534: Ullrich again goes quickest at the second time check with a time of 35mins 19secs, but the German has not really increased his pace since Chemere.
1522: At the second time check, Tyler Hamilton moves into second place behind Millar.
1518: Armstrong goes through Chemere in exactly the same time. There is nothing between these two riders.
1515: At the first time check at Chemere, Ullrich goes fastest so far at 15mins 42secs, 12secs better than the previous best by Owe Paschal.
1513: Ullrich has a scare as he looks slightly unsteady going through a big puddle.
1506: Both riders look strong early on as the weather shows no sign of improving.
1501: The last rider and four-time Tour champion Lance Armstrong leaves the podium in Pornic. The race is on.
1459: With the pressure on, second-placed Jan Ullrich goes off to huge cheers.
1456: Third-placed Alexander Vinokourov sets off. The Russian is 2mins 47secs behind Armstrong.
1447: American Tyler Hamilton - in sixth place overall despite a broken collarbone - sets off as the atrocious conditions continue to make life difficult for everyone.
The riders are having to strike a delicate balance between taking risks to make time and staying on their bikes.
1436: With half an hour left until Armstrong and Ullrich go out, no rider can get anywhere near Millar's time.
1421: German time trial specialist Uwe Peschel has broken a rib after twice falling off during the stage. He posted the fastest time at the first time check and although he managed to finish the course he is outside the top five.
1406: George Hincapie, a US Postal team-mate of overall leader Lance Armstrong, posts the fifth fastest time, over a minute behind Britain's David Millar.
1350: 92 of the 148 riders left in the race have now completed the time trial, but the big guns have yet to get going.
1345: Millar races into an excellent lead despite falling off, taking 26 seconds out of the previous best by Hungary's Laszlo Bodrogi, with a gritty display. His time of 54mins 05secs will take some beating.
1339: Millar stretches his lead at the third time check at Bougenais, leading time trial specialist Vjatceslav Ekimov by 45 seconds.
1325: Britain's David Millar makes a very encouraging start setting the quickest time at the second time check at Bouaye.