We studied the prognostic value of sperm characteristics for the outcome of intra-uterine insemination with partner sperm (IUIPS). A total of 712 cycles of IUIPS following induction of ovulation with gonadotrophin (hMG/hCG) for 277 sterile couples attending the assisted reproductive technology centre of Poissy Hospital (78300-France) between January 1991 and December 1994 was studied retrospectively. Ninety-two clinical pregnancies were obtained giving an overall rate of 12.9% per cycle. None of the characteristics of the sperm as assessed initially correlated with outcome. In contrast, the number of motile spermatozoa given (n) affected outcome: for n < 1 x 10(6) the pregnancy rate was 2%; for n = 5 to 8 x 10(6) the rate was 19%. However, for +/- 8 x 10(6) the proportion of biochemical pregnancies and miscarriages was 40% which was significantly higher than for smaller concentration. The resort of IVF following 4 IUIPS failures leads to a pregnancy rate per cycle of only 6.7%.