Testosterone was measured through three consecutive years in sera from young and adult male subjects working in a chemical factory exposed to some complex chemical noxae, the major exposure being acrylonitrile (vinylcyanid). In the first yr, (group A), the blood was collected on May 1975 (no 39), the II-nd yr (group B) on March (no 109) and the III-rd yr (group C) on May (no 149). The exposure time varied in each group between 6 mos and 7-10 yrs. For comparison, blood samples were collected from 145 men of comparable age grouped in nonexposed: blood donors (no 37) (group a), new workers (no 23) (group b) and exposed to other chemical noxae in the same factory: Na cyanid (group c, no 23), cyan derivatives (group d, no 22) and pyrolysis (group no 39). The seasonal testosterone variations being considered, the Student's 't' test applied to the hormonal levels in acrylonitrile groups A, B and C showed non significant differences. However, the comparison of the testosterone concentrations in sera of the groups A, B and C vs the control groups investigated during the same month of the year showed much lower levels of the hormone in the first groups (p less than 0.001). These data are suggesting that the exposure to acrylonitrile either by direct participation to the technological chain or by working in the same noxious environment may influence the testosterone synthesis and/or secretion.