Hormonal and semen parameters in 416 men aged 25-45 years were examined: 328 were men who cleaned the territory around the Chernobyl nuclear reactor (called 'liquidators') and 88 were healthy age-matched controls. The dose of radiation received by the liquidators was 0.16 +/- 0.08 Gy. LH, FSH, prolactin, testosterone and cortisol levels were assayed using WHO-matched reagents. Semen analyses were performed according to the WHO Manual (1992). The mean concentration of all hormones in liquidators and controls were within the WHO-defined normal range. The mean levels of LH and cortisol in liquidators were significantly lower (p = 0.013 and p < 0.001, respectively) and testosterone significantly higher (p = 0.023) than in controls. The variations in hormone levels in liquidators were not correlated with the acquired doses of radiation as measured by personal dosimeters (film badges). Semen parameters in a subgroup of 70 liquidators were within the normal WHO-defined range. The percentage of normal forms of spermatozoa in liquidators (35.0 +/- 13.1%) was significantly lower (p < 0.015) than in a control group (42.8 +/- 8.9%). The study has shown that exposure of men to relatively short-term radiation did not cause long-lasting disruption of their endocrine status and spermatogenesis. The study was 7-9 years retrospective and it is therefore impossible to infer what the immediate effects of the radiation exposure were on these parameters.