The air in a factory producing N,N' methylene-bis-(2-amino-1,3,4-thiadiazole) (MATDA) and water in a nearby river were often polluted by the intermediate and finished product. The levels of MATDA in the air, soil, and river water were 0.1-0.8 mg/m3, 6-2 650 mg/kg, and 0.5-2 mg/kg, respectively. Seventy-nine workers engaged in MATDA production were observed; 44% of them suffered from contact dermatitis; and 72% showed changes of pigment in the skin (versus 2 and 16%, respectively, for the referents). All of the exposed workers had experienced dermatitis at some time. For 218 pupils of a primary school in the neighborhood of the factory, the incidence of hypopigmentation and pigmentation of the skin was 14 and 72%, respectively, but in the reference group the corresponding incidence rates were 0 and 20%. Pigment changes of workers' children increased with the duration of residence in the neighborhood of the factory. The results of the survey led to a change in the formulation of the product from a powder to an emulsion. Improved technology was also initiated which allowed most of the waste to be reused in the processing. After these control measures the dermatitis of the workers was greatly reduced.