Acute graft-versus-host reaction after allogeneic bone marrow transplantation has been reported to induce toxic epidermal necrolysis. To assess the respective role of acute graft-versus-host disease and of drug reaction in this setting, we retrospectively reviewed nine cases of toxic epidermal necrolysis that occurred in a series of 152 allogenic bone marrow recipients. In five cases visceral involvement was suggestive of acute graft-versus-host disease without any drug more than "doubtfully" suspected. In four cases extracutaneous symptoms were absent or mild and suspect drugs (mainly sulfonamides) had been administered with a timing suggestive of "possible" causality. All nine patients died, mainly from infection possibly aggravated by high doses of corticosteroids. We conclude that toxic epidermal necrolysis may be more frequent than generally thought after bone marrow transplantation and has a poor prognosis. It seems to be related to a drug reaction to sulfonamides as often as to acute graft-versus-host disease.