Sera were obtained from 266 mothers of singleton stillborn babies (cases) and 266 mothers of live-born babies (controls), matched for parity, who delivered at the University Teaching Hospital, Lusaka, Zambia, between October 1979 and April 1980. Tests were performed on 262 samples from cases and 261 from controls. The microhaemagglutination assay for Treponema pallidum (MHA-TP) was reactive in 54% of cases and 29% of controls; the rapid plasma reagin (RPR) 18-mm circle card test was reactive at a dilution of 1:16 or greater in 29% of cases and in 3.5% of controls. Both these differences are highly significant.Sera from cases and controls were further examined for evidence of cytomegalovirus, human (alpha) herpesvirus, hepatitis B virus, toxoplasma, and plasmodium infections. The only difference between sera from cases and controls was that cytomegalovirus antibody titres >/= 1:1024 occurred more often among cases. There was no relationship between antibody titre and birth weight.The results of this study emphasize the importance of screening pregnant women for syphilis. Treatment of those found to be infected should help prevent stillbirths due to syphilis.