There are controversial data on the effects of stress on semen quality during treatment for infertility. We have compared the parameters of semen obtained from 84 patients on the day of the ovocyte pick-up during an in vitro fertilization and embryo transfer program (IVF) with those of semen collected from the same patients on the day of admission to the program (up to 3 months earlier). Abnormal semen has been found in 2 of the 84 patients on the day of admission and in 11 on the day of IVF. There were no improvements in semen quality of any patient at the second test. All except two parameters evaluated objectively by the Hamilton-Thorn Motility analyzer were significantly worse (p < 0.001) on the day of IVF, the exceptions were the percentage with moderate or slow motility and the Linear Index. These data indicate that the emotional stress to a subject enrolled in an IVF program negatively affects the quality of semen. Some suggestions are made for improved management of these patients.