A comparison of semen parameters from 25 workers at a reinforced plastic production plant and from 46 age-matched male fertility patients was carried out. For a period of more than three months before the semen analyses, the 25 workers had been exposed to styrene and acetone in concentrations exceeding the Danish threshold limit values. Serum concentrations of follicle stimulating and luteinizing hormones, semen sample volume, and concentration of sperm showed no differences between the two groups. Significant differences between the two groups were found in the percentage of live sperm, immotile sperm, and normal sperm. The reinforced plastic plant workers showed, in terms of semen quality, better values in the percentages of live sperm and immotile sperm, whereas they had a reduced percentage of normally shaped sperm. It was found that the reinforced-plastic workers had increased percentages of the amorphous and the pyriform sperm head shapes as compared to the fertility clientele. In sperm midpiece and sperm tail defects, the two groups showed similar values. From the data it could be concluded that work with production of reinforced plastic might result in an increase in the number of abnormal sperm heads.