In considering the relationship between the occurrence of allergic diseases and the environment, much attention should be given to the patient's hypersensitivity to drugs. This is bectuse these diseases could occur in a medical environment, especially due to therapeutic drugs given. In addition, drug hypersensitivity has beecome an important problem these days as the drug therapy has greatly expanded. Although drug eruption is the most frequent result of drug hypersensitivity, a very reports have been published on the studies of drug eruption from a psychosomatic viewpoint. The present study deals with the results of a clinical investigation of drug eruption from a psychosomatic viewpoint. The following results were obtained : 1) The incidence of drug eruption was 101 out of 1578 cases in a medical outpatient clinic (6.4%). The incidence was two times higher in females than in males. There were a variety of causative drugs, including pyrazolone analgesics, antibiotics, non-steroidal antiinflammatory drugs and others. 2) The patients with drug eruption showed a high rate of neurotic tendency which was estimated by the Cornell Medical Index as well as of allergic factors which were examined by both the candida skin test and serum lgE Ievels. The cases whose eruption was caused by only one drug were mainly of allergic origin. In contrast, the cases of drug eruption due to two or more drugs showed a tendency to have both neurotic and allergic factors. 3) Drug eruptions weve tentatively classified into three types, designated as allergic, bsychosomatic and neurotic, according to the presence or absence of neurotic and allergic factors. In addition, psychosocial factors were analysed in the individual patients in relation to the pathophysiological mechanisms of drug eruption. The results are suggestive of the following psychosomatic mechanisms for drug eruption : Psychosocial factors (1) may affect the autonomic nervous reaction or the vasomotor reaction ' which lead to skin rash, (2) may cause an imbalance in the central nervous function which affects the neurohumoral mechanism of drug eruption, and (3) may influence the attitude of patients in taking medicine and may aggravate the drug eruption.