The present report examines retrospectively the success rates of both in-vitro fertilization and embryo transfer (IVF-ET) and gamete intrafallopian transfer (GIFT) in relation to the underlying infertility disorder. Reduced fertilization rates were seen when the male partner was oligospermic or had both IgA and IgG in his semen, or the female partner had elevated LH concentrations during the follicular phase. In IVF-ET, the chance of pregnancy was reduced in women with elevated LH concentrations or endometriosis. Pregnancy rates for patients treated in the GIFT program were significantly better (P less than .001) than for those treated by IVF-ET. Of special interest was the finding of an improved chance of pregnancy for patients with severe endometriosis treated by GIFT (P less than .001). With oligospermia, pregnancies were only achieved in the GIFT program when the insemination number was increased. The pregnancy outcome was similar in both programs, with approximately 70% of pregnancies delivering beyond 20 weeks' gestation. However, there was a high rate of ectopic pregnancy, particularly in cases with underlying tubal disease. These findings have led to revised guidelines for the accurate counseling of patients, and provide further insight into the possible mechanism of various disorders contributing to infertility.