A double blind controlled trial was carried out to investigate the method of controlling neonatal staphylococcal disease (NSD) by passive immunization. A group of 166 pregnant women were randomly immunized with a monovalent capsular polysaccharide antigen or with poliomyelitis vaccine (Salk-type) used as "placebo." After delivery, mothers and babies were followed-up at weekly intervals for six weeks. Episodes of staphylococcal disease were recorded. Staphylococcal hemagglutinating antibodies (SHA) were measured in blood specimens collected from mothers and babies before immunization, at birth, and six weeks after birth. The results showed no demonstrable protecting effects against NSD, while paired seras had high levels of SHA titers. This lack of success is ascribed to the type of vaccine used. Further trials with an improved polyvalent capsular staphylococcal antigen are recommended.