The clinical value of two inexpensive and easy to perform sperm function tests (hypo-osmotic swelling and bovine sperm mucus penetration tests) were examined in a prospective study of in-vivo conception rates in 325 couples. Both tests were of no significant value alone or in combination with traditional semen characteristics in predicting pregnancy outcome. The two most predictive factors of conception were the length of infertility and percentage of progressively motile spermatozoa. Our data support the further investigation of sperm function using more sophisticated quantitative tests, specifically the examination of sperm motility.