The efficiency of the transfer of information among doctors about current drug therapy was examined in emergency, waiting list, and outpatients. Communication about the patient's recent medical history was established with the practitioner in 551 of 559 patients referred (99%). Four hundred and ninety-eight patients (89%) were currently taking 1,557 drugs either supplied by prescription or taken as self-medication. In 314 patients (56%) some information was supplied by the practitioner about 555 drugs (36%). Six hundred and thirteen (61%) of the 1,002 drugs not mentioned by the practitioner were drugs supplied by prescription, mainly hypnotics, sedatives, and analgesics. The transfer of information was unsatisfactory about drugs taken as self-medication and about the allergic status of patients.If iatrogenic disease due to drug therapy is to be recognized or prevented the communication of information about drugs must be improved.