The minimum value for each of the five main semen parameters, below which conception rarely occurred or did not occur at all, was calculated in a group of 1884 couples complaining of primary and secondary infertility: 304 conceptions including first as well as consecutive conceptions, occurred. The parameters evaluated were (minimum value calculated in this study between brackets) volume (1.0 ml), sperm count ml(-1) (2.0 million), total sperm count (4.0 million), motility (10%), forward progression (2.0 MacLeod units: scale 1-4) and normal sperm morphology (3%). The pregnancy rate in the group of 308 oligozoospermic men and the minimum value of semen parameters were the cornerstones in determining the prognosis for oligozoospermic patients. A sperm count of >2.0 million ml(-1) was considered relatively adequate for eventual conception judged by the 68 of 308 (22.1%) pregnancies that occurred among oligozoospermic men in this study, provided that the other five semen parameters showed values above the minimum value. In cases where the average sperm count was <2 million ml(-1), the chances for conception became rare, viz five of 308 (1.6%). The total number of pregnancies in the group classified as oligozoospermic was 73 (23.7%). With these pregnancies there was no increase in the rate of foetal wastage and congenital abnormalities. Abortion occurred in 15.09% and ectopic pregnancy in 0.9% among first and consecutive pregnancies. One infant among the 56% boys and 44% girls was born with congenital abnormalities. Most of these infants had a normal birth mass of >2500 g.