A cross-sectional study of 68 petrochemical workers(23had never smoked [E/NS],45 were current smokers [E/S]) and 130 subjects with no known history of exposure to petrochemicals (49 had never smoked [NE/NS], 81 were current smokers [NE/S]) was conducted to assess the effect of occupational exposure to petrochemicals and smoking on semen quality.In-person interviews revealed occupational history,smoking habit,and lifestyle.Semen parameters such as volume,viability,sperm forward progression rate,sperm density,and total sperm count were determined for all subjects.The results show that the E/NS workers had a lower sperm forward progression rate (P<0.05) compared with controls (NE/NS). Individuals in the NE/S group showed a significant inverse relationship between years smoked and sperm density (r=-.24,P<0.05). The data also revealed that cigarette smokers who had worked in a petrochemical plant had significantly poorer quality semen,including sperm density,total sperm count,and forward progression rate, compared with the control (NE/NS)group (P<0.01). Furthermore, there was a significant inverse correlation between combined exposure and smoking years,and sperm density (r=-.28, P<0.05). These findings suggest that occupational exposure to petrochemical compounds may aggravate the adverse effect that smoking has on semen quality.