In order to assess the degree of thallium exposure in a population living around a thallium emitting cement plant in a small city in North-West Germany thallium levels in 24 h urine samples of 1,265 subjects and in hair samples of 1,163 subjects were determined. Urinary thallium levels in two groups of subjects living in an urban and a rural area of West Germany were determined for reference. As compared to these subjects the population living around the cement plant exhibited obvious signs of increased thallium intake. The mean urinary thallium concentration was 2.6 micrograms/l and ranged up to 76.5 micrograms/l. In contrast, the mean urinary thallium levels of the two reference groups were 0.2 and 0.4 micrograms/l, respectively. Hair thallium levels of the population living around the cement plant were also markedly increased (mean: 9.5 ng/g). The major route of the population's increased intake of thallium was found to be the consumption of vegetables and fruit grown in private gardens in the vicinity of the cement plant. As was shown by chemical analyses vegetables and fruit grown in these gardens were contaminated by thallium-containing atmospheric dust fall-out caused by emissions of the cement plant. The pulmonary route of uptake as well as other sources did not seem to play a significant role in the population's exposure to thallium. Polyneuritic symptoms, sleep disorders, headache, fatigue and other signs of psychasthenia were found to be the major health effects associated with increased thallium levels in urine and hair. No positive correlation was found between the thallium levels in hair and urine and the prevalence of skin alterations, hair-loss and gastro-intestinal dysfunctions.