A survey of twenty-six cases of erythema multiforme was undertaken. All patients had oral lesions and seventeen had skin involvement, mainly on the hands. The average age was 32 years, and female patients predominated in the group. Nearly one third gave a history of a severe emotional disturbance prior to the attack, four patients developed lesions after penicillin therapy, and two presented initially with acute primary herpes simples stomatitis. Skin and mucosal biopsies were undertaken in some patients, and it was concluded that no pathognomonic features were identifiable; a subepithelial bulla, however, could occasionally help in the differential diagnosis. Other laboratory investigations, including a complete blood count, determination of herpesimplex titer, and urinalysis, were not helpful, except that the erythrocyte sedimentation rate was raised in sever cases. Possible etiologic factors were discussed in relation to the survey. It was thought that the cause is still obescure except in drug-induced cases and that the diagnosis is essentially a clinical one, since various laboratory investigations cannot be shown to produce consistent pathognomonic findings.