Blood lead (BPb), actity of 6-aminolevulinic add dehydratase (ALAD), erythrocyte protoporphyrin (EP), blood cadmium (BCd), serum zinc (SZn), seminal fluid zinc (SaZn), serum copper (SCu), and parameters of semen quality and of reproductive endocrine function were measured in 149 healthy male industrial workers 20-43 years of age. The group contained 98 subjects with slight to moderate occupational exposure to Pb and 51 reference subjects. All of the subjects lived in Zagreb, Croatia. Significant (p < 0.05) correlations of BPb, ALAD, and/or EP with reproductive parameters indicated a Pb-related decrease in sperm density, in counts of total, motile, and viable sperm, in the percentage and count ofprogressively motile sperm, in parameters ofprostate secretory function (S£Zn, acid phosphatase, and citric add in seminal fluid), and an increase in abnormal sperm head morphology, serum testosterone, and estradiol. These associations were confirned by results of multiple regression, which also showed significant (p < 0.05) influence of BCd, SZn, SCu, smoking habits, alcohol consumption, or age on certain reproductive parameters. These effects were mainly of lower rank and intensity as compared to Pb-related reproductive effects, whereas BCd contributed to a decrease in sperm motility and an increase in abnormal sperm morphology and serum testosterone. No significant Pbor Cd-related influence was found on levels of the lactate dehydrogenase isoenzyme LDH-C4 and fructose in seminal fluid or on follide-stimulating hormone, luteinizing hormone, and prolactin in serum. The seminal fluid concentrations of Pb (SfPb) and Cd (SfCd) were measured in 118 of the 149 subjects, and a highly significant (p < 0.0001) correlation was found between BPb and SfPb levels (r = 0.571) and between BCd and SfCd levels (r-=0.490). The overall study results indicate that even moderate