Thiourea compounds are mainly used as accelerators in the rubber industry, but also in other industries, e.g., as antioxidants in the graphics industry. Thiourea compounds may provoke allergic contact dermatitis, although the number of reported cases is relatively low. During 1985-1991, we had 5 patients with allergic patch test reactions caused by thiourea compounds. 1 of our patients had to use a knee brace after an occupational accident. He developed allergic contact dermatitis caused by the knee brace, probably because he had become sensitized to diethylthiourea. 2 patients were probably sensitized by diphenylthiourea in neoprene gloves. A florist had an allergic patch test reaction to diphenylthiourea and might have been sensitized by fungicides or pesticides, which break down into thioureas. It is often difficult, however, to detect the source of thiourea compound sensitization. If the patient has contact dermatitis and has been exposed to products that may contain thiourea compounds (or compounds that break down into thiourea compounds), such as rubber, PVC plastic or adhesive, diazo paper, paints or glue remover, anticorrosive agents, fungicides or pesticides, patch testing with a series of thiourea compounds needs to be performed. If patch testing with thiourea compounds is not performed, allergic contact dermatitis caused by thiourea compounds is not likely to be diagnosed.