The cryoprotectant dimethyl sulfoxide (DMSO) is known to have toxic side effects, yet guidelines for its use in stem cell transplantation do not exist. To assess current practice in the use of DMSO and the incidence of DMSO-related complications, a single page questionnaire was mailed to 444 EBMT centres involved in autologous transplantation. The responses from 97 centres showed a wide variation in practice between transplant units regarding the concentration of DMSO used, daily DMSO dose restriction and the use of cell washing. The overall incidence of DMSO toxicity was approximately one in 70 transplants and most cases were cardiovascular and respiratory in nature. There was a trend to reduced complication rates in centres using lower concentrations of DMSO or washing cells prior to return. A large-scale prospective study of the strategies for reduction in exposure to DMSO and reduction in toxic effects is required before guidelines in the use of DMSO in stem cell cryopreservation can be promulgated.