In 73 hairdressers, out of a total number of 3,300 patients, patchtests were performed using substances of a standard series. Patients of various professions excluding hairdressers and patients belonging to an age group comparable with that of hairdressers, served as two control-groups. In the group of hairdressers the most frequently seen positive reactions were against p-phenylendiamin, nickelsulfat, pellidol, cobaltchlorid, p-aminodiphenylamin, and perubalsam. The incidence of positive reactions against p-phenylendiamin and pellidol in this group was significantly higher than in the control group, whereas the higher incidence of nickelsulfat allergy in hairdressers proved not to be significant.