OBJECTIVE--To compare the cumulative pregnancy rates after gamete intrafallopian transfer (GIFT) with the cumulative spontaneous pregnancy rates in couples with unexplained infertility. DESIGN--A contemporaneous study in a single group of patients. SETTING--Northern Regional Fertility Centre. SUBJECTS--76 couples with unexplained infertility of more than 3 years duration. INTERVENTIONS--Successful pregnancies were recorded during at least 3 months before GIFT and up to 21 months after a maximum of three cycles of GIFT treatment. MAIN OUTCOME MEASURES--Pregnancy resulting in a live birth. RESULTS--Average monthly fecundability without treatment was 0.021 and after GIFT was 0.14 (P less than 0.001). This was reflected as a cumulative pregnancy rate of 52% after three cycles of GIFT and 30% after 24 months without treatment. CONCLUSIONS--The chance of having a baby after one cycle of GIFT is significantly greater than the chance in a spontaneous cycle. However, considering the cumulative pregnancy rates, we suggest that if GIFT is to be a realistic treatment option, it should be offered for more than one cycle.