Twenty-nine infertile couples were treated by intrauterine insemination (IUI) of washed sperm from a sub-fertile husband (n = 16), in cases of gynaecological (n = 3), combined (n = 4) or idiopathic (n = 6) infertility; 116 treatment cycles resulted in 11 ongoing pregnancies. Between 0.25 and 0.45 ml of capacitation medium, containing at least 500,000 pretreated spermatozoa, were inseminated. Pre-treatment of first split fractions was performed by centrifugation and swimming up of motile spermatozoa. The pregnancy per cycle index (P/C) for IUI was 9.5% for a total of 37.9% of all couples treated achieving pregnancy. These results suggest a substantial benefit compared with a calculated six months' cumulative pregnancy rate of 4.2% independent of treatment, for this infertile population. The value of IUI in selected cases of infertility seems obvious but needs further investigation.