OBJECTIVE In recent years, there have been many nonconclusive studies on cigarette smoking and sperm quality. Few studies, if any, have attempted to implicate any decrease of sperm quality. The aim of this study was to examine the relationship between cigarette smoking, blood and seminal plasma concentrations of cadmium and lead, and sperm quality. METHODS A total of 184 males who were undergoing initial screening for infertility were included in the study. Tests conducted included semen characteristics (volume, total sperm count, sperm viability, motility and morphology of spermatozoa), and blood and seminal plasma concentrations of lead and cadmium. RESULTS More than 50% and 70% of the subjects had normal sperm density and motility, respectively. The mean concentrations of lead in blood (PbB) and seminal plasma (PbS) were 7.09 micrograms/dL and 12.98 micrograms/L, respectively, while the mean concentrations of cadmium in blood (CdB) and seminal plasma (CdS) were 0.95 micrograms/L, and 0.58 micrograms/L, respectively. Significant correlations were observed between CdB and cigarette-years and sperm density (negative). CdS was significantly correlated with cigarette-years and sperm volume (negative). Significant trends were observed for different categories of cigarette-years with CdB, CdS and sperm density. CONCLUSIONS Cigarette smoking appears to affect sperm density, especially in heavy smokers. Cadmium (present) in cigarettes could be a possible causative agent for the low sperm density among smokers.