From 1979 to 1981, several medical surveys were carried out among a population living in the vicinity of a cement plant that emitted dust containing thallium until August, 1979. Air, soil, plants, and domestic animals in the area were contaminated by thallium and this led to an increased intake of thallium in the population, mainly due to the consumption of home-grown vegetables and fruit. In order to assess the degree of the individuals' exposure to thallium, thallium levels in 24-h urine samples (TlU) were determined. Three surveys were carried out from September to December, 1979 to assess the degree of thallium exposure of different parts of the general population. Subjects with relatively high exposure, as indicated by the results of the above mentioned population surveys, or those suffering from health disorders that might be related to an increased intake of thallium, were reexamined several times from 1979-1981. Special attention was also given to children attending a kindergarten situated about 0.5 km from the cement plant. As compared to an "unexposed" reference population (mean TlU: 0.3 microgram/l), the majority of the population living in the cement plant area had significantly elevated urinary thallium levels (range: less than 0.1-76.5 micrograms/l) indicating a substantially increased environmental exposure. A reduction of the intake of thallium was mainly achieved by the fact that the population, as advised by the authorities, largely avoided the consumption of home-grown, potentially contaminated foodstuffs. Reports on the teratogenicity of thallium in certain animal species caused great concern that thallium might have exerted teratogenic effects on the newborn of women exposed to thallium during pregnancy. Therefore, an investigation of children born between January, 1978 and August, 1979 (n = 297) was carried out. Although the number of congenital malformations was greater than expected, we conclude, considering carefully all data available, that there is likely no causal relationship between thallium and the occurrence of congenital malformations in the children investigated.