The effects of toxic agents on the male reproductive system were reviewed in a retrospective study. An assessment profile used by NIOSH was described as a necessary step in assessing populations at risk of exposure to potential reproductive toxicants. Emphasis was placed on assessing parameters of fecundity rather than fertility in considering the reproductive effects of exposure. The reproductive profile in human toxicology studies was discussed and included semen analyses, sperm viability, measurements of sperm motility and velocity, and sperm morphology analysis. The impact of toxic exposure on several aspects of male reproductive functions were discussed: toxic effects on male reproductive systems have been observed in the neuroendocrine system, the testes, the accessory sex glands and sexual functions. The reproductive endocrine status can be determined by measuring levels of follicle stimulating hormone, luteinizing hormone, testosterone, and prolactin in circulation or in the urine. Though seminal plasma is not essential for fertilization, it does facilitate sperm transport. For this reason, biochemical analysis of seminal plasma has been performed to study the function of the accessory sex glands. Erection assessment and ejaculate volume have been studied as measures of the combined influences on sexual function. Previous studies into male fecundity relating to occupational exposures have been performed for heavy metals, pesticides, ethylene-dibromide (106934), and solvents. Environmental exposures have also been reported in a few studies; however, this has been rare due to the difficulties in characterizing populations and assessing exposure levels.