The aim of this study was to compare the probability of survival of infants born to anti-HIV-1-positive and anti-HIV-1-negative mothers. One thousand, eight hundred and thirty-three pregnant women, recruited sequentially in two mother-child clinics in Brazzaville, were screened for anti-HIV-1 (by enzyme-linked immunosorbent assay with confirmation by Western blot). Each seropositive mother (71 out of 1833, 3.9%) was matched for age, presumed date of delivery and place of residence with two seronegative mothers. Sixty-four babies born to anti-HIV-1-positive mothers and 130 control babies born to anti-HIV-1-negative mothers were followed up for 12-22 months (mean, 18 months). The probabilities of survival were estimated by the Kaplan-Meier method. At birth, the two groups of babies did not differ with regard to rate of stillbirths, gestational age, sex ratio and weight. Among babies born to seropositive mothers, the probability of survival was 0.87 (s.d. 0.04) at 3 months, 0.71 (s.d. 0.06) at 6 months, 0.68 (s.d. 0.06) at 9 months and 0.61 (s.d. 0.06) at 12.5 months. In the controls the probability of survival was 0.98 (s.d. 0.01) at 3 months and 0.97 (s.d. 0.02) at 12 months. The excess of mortality in the babies born to anti-HIV-1-positive mothers is highly significant (P less than 0.001). The deaths occurred more frequently and earlier than in similar cohort studies performed in developed countries.