Evaluation of the male factor in infertility is becoming increasingly important as new diagnostic techniques and therapeutic options become available. Varicoceles are among the most common treatable cause of male infertility. Varicoceles are present in 10% to 20% of all males but are found in as many as 30% to 40% of men who present to an infertility clinic. Of men who have treatment for varicoceles, 50% to 75% will show some improvement in semen quality, and 30% to 40% will initiate a pregnancy. We review some controversial issues related to the diagnosis and treatment of varicoceles. In vitro fertilization, originally developed for the female with irreversible tubal damage, is now being evaluated as a possible therapy for severe male-factor infertility that has failed to respond to routine surgical or medical treatment. In vitro fertilization for the oligospermic male, however, is further complicated by the fact that men with poor sperm production frequently have poorly functioning sperm as well. Consequently, we discuss the value of the sperm penetration assay, with and without enhancement techniques to prospectively evaluate couples entering in vitro fertilization programs. We also discuss the role of strict criteria for determination of sperm morphology and quantitation of leukocytospermia in the evaluation of the infertile male. Finally, evaluation of the predictive value of "failure to fertilize" at in vitro fertilization for future in vitro fertilization success is discussed.