Former World Sidecar champion Ben and Tom Birchall were airlifted to hospital following a crash during practice at the Isle of Man TT on Monday evening.
The pair were involved in an incident at Brandywell and were reported to be conscious at the scene before they were taken to Nobles Hospital in Douglas.
Glyn Jones and Richard Murphy were also involved in a crash at Keppel Gate on the Mountain course.
The pair, described as conscious at the scene, were also transported to hospital by helicopter.
Sidecar ace Dave Molyneux and Patrick Farrance led the times at 111.856mph from Tim Reeves and Dan Sayle at 110.748mph.
Passenger Sayle, a former TT winner in the Sidecar class, had vowed to skip the 'chairs' races this year to concentrate on competing in the solo races, but agreed to partner Reeves after his original passenger, Dipash Chauhan, opted to pull out of TT2012 due to the effects of a leg injury sustained last season.
Molyneux, who has 14 victories at the TT in the Sidecar class, returns this year after sitting out the event in 2011.