From 1984 to 1986, 172 couples were enrolled in an artificial insemination homologous (AIH) program, because of negative postcoital test, fair PT, positive PT with unexplained infertility, and impotentia coeundi. Patients were randomly assigned to the following procedures: AIH with native semen (N, n = 68), washed sperm (V, n = 50), semen mixed with kallikrein (K, 5 IE/ml semen, n = 45), and timed intercourse. The overall pregnancy rate (PR) was 22% per couple (13% inseminations, 9% spontaneous). PR from insemination (spontaneous) was 13% (8), 13% (13), 23% (0) in PT negative, fair, and positive patients, respectively, and 18% (9), 13% (7), and 11% (9) in AIH groups N, V, and K. Among in vitro studies with K added semen, an improvement of sperm motility was demonstrated in half of the specimens. In the capillary tube test (CTT), with wives' cervical mucus, a deterioration was more frequently seen than an improvement after 2 h, independent of the early effect of K in semen, K induced changes of CTT were less pronounced when donors' cervical mucus was used. The results of the in vitro studies offer an explanation for the low PR in the AIH program with K.