The prevalence of transplacental transfer of microfilariae and structural lesions in the placentas of amicrofilaraemic (n = 10) and Wuchereria bancrofti microfilaraemic (n = 10) pregnant women from the prenatal care unit of the Hospital das Clinicas, Recife, Brazil, was investigated. Study participants were selected by filtration (3 microns/13 mm) of nocturnal (2300-0100 h) venous blood. A detailed histopathological examination was performed to detect abnormalities in the placenta, the cord and the foetal membranes. Both study groups had similar obstetric profiles. Parasitaemia was present during labour in nine of ten microfilaraemic women, but no microfilariae were found by filtration of 5-10 ml cord blood. No macroscopic abnormalities were seen in placentas from microfilaraemic mothers; two placentas from the amicrofilaraemic cases contained, respectively, infarcted areas and cysts at the cut surface. Microscopy failed to detect microfilariae in the intervillous spaces, chorionic and decidual vessels, or the umbilical cord. Thus, transplacental transfer of Wuchereria bancrofti microfilariae seems to be a rare phenomenon, and microfilaraemia does not appear to be a risk factor for placental pathology.