The results of 109 intra-uterine inseminations with cryopreserved prepared donor semen (IUId) in stimulated cycles, performed among 42 couples from November 1987 to June 1991, were analysed. The single IUId was performed 39 +/- 3 hours after the injection of human chorionic gonadotrophin. For each IUID 1,25 +/- 1.4 x 10(6) motile spermatozoa (mean +/- standard deviation) were inseminated. 27 pregnancies were obtained and the pregnancy rate per cycle was 24.8%. The number of motile spermatozoa inseminated was significantly higher in the group of pregnant women than in the population without pregnancy (1.64 x 10(6) x 10(6)/IUI versus 1.13 x 10(6)/IUI). The sperm count and the number of motile spermatozoa inseminated were significantly higher when the semen was prepared on discontinuous Percoll gradients than after swim-up in Menezo B2 medium (8.2 x 10(6)/ml versus 4.3 x 10(6)/ml and 1.7 x 10(6) versus 0.77 x 10(6)). Among the 27 clinical pregnancies, 3 were twins and 2 were triplets. The ovarian hyperstimulation associated with the use of a prepared semen of donor, generate a high risk of multiple pregnancies. To improve the results without increasing the risk of multiple pregnancies, we propose to inseminate about 1.5 x 10(6) motile spermatozoa with a maximum plasma estradiol level of 1 100 pg/ml, on the day of hCG injection, associated with 2 preovulatory follicles. This technique may augment the rate of pregnancy and represents an appreciable time gain. These results must be confirmed by randomized prospective studies.