Abstract. Antibodies to Schistosoma mansoni were detected by slide flocculation (the Plasma Card test) in umbilical-cord blood of 33 of 100 newborn infants in St. Lucia, West Indies. The mothers of these 33 infants were also seropositive to this test. The reactions of 19 pairs of sera from mothers and infants were confirmed in the fluorescent antibody test. At the end of 6 months, none of 31 infants seropositive at birth had detectable antibodies.