Determinations of transferrin (Tf), fructose (Fru), citric acid (CA), zinc (Zn) and copper (Cu) levels of seminal plasma in 38 male workers exposed to mercury vapor and 18 male unexposed controls showed levels of Tf and total Fru, and sperm density adjusted Fru level of seminal plasma in workers exposed were significantly lower than those in controls, and the latter lowered gradually with increase of exposure to mercury. No significant difference of levels of CA, Zn and Cu of seminal plasma between the two groups was found. It suggests chronic exposure to mercury vapor may cause adverse effects on Sertoli's cells of spermatogenic epithelium and seminal vesicle function.