In vitro fertilization (IVF) and GIFT have been proposed as therapeutic approaches in infertile couples where a significant male factor is present. To date, few published data are available relating the success rate of GIFT to the severity of the male factor. In this report the results of the first 172 GIFT cases were analyzed. The overall pregnancy rate was 18.0%. The relationship between the occurrence of pregnancy and sperm count (millions/ml), total sperm count (millions/ejaculate), % motility, motile sperm count (millions/ml) and total motile sperm count (millions/ejaculate) were examined. Significant direct correlations were observed between the clinical pregnancy rate and sperm count, total sperm count, motile sperm count and total motile sperm count. Motile sperm count and total motile sperm count had the best correlations with clinical pregnancy rates, which were over 24.0% in groups with motile sperm counts exceeding 40 X 10(6) cells/ml or total motile sperm counts greater than 100 X 10(6)/ejaculate. The clinical pregnancy rates were 12.5% and 7.7%, respectively, for groups with motile sperm counts under 10 X 10(6)/ml and total motile sperm counts below 25 X 10(6)/ejaculate. No correlation was found between percent motile cells and pregnancy rate. Results of the sperm penetration assay using zona-free hamster eggs were available in a subpopulation of 27 patients. No significant correlation between this sperm penetration assay and pregnancy rate could be demonstrated. The incidence of chemical pregnancy showed a significant negative correlation with the total motile sperm count, indicating a higher incidence of early pregnancy wastage in cases of oligozoospermia.(ABSTRACT TRUNCATED AT 250 WORDS)