Eighty-two neonates suffering from widespread infection detected at an early stage were treated either with antibiotics alone or with antibiotics combined with immunoglobulins administered intravenously. In 35 children, haemocultures demonstrated septicaemia due to E. coli, Klebsiella spp., staphylococci or anaerobes. Following a 6 days' treatment with immunoglobulins i.v. (0.5 g/day in prematures and 1.0 g/day in children born at term) serum IgG levels were considerably increased. Already in children born in the 28 th week of gestation IgG levels were similar to those of children born at term. This increase in serum IgG's resulted in a 26% to 10% (p = 0.16) overall fall in death rate. In prematures, the death rate, which was 44% in children who had not received IgG's, fell to 8%. In 47 neonates without septicaemia the death rate was 15% without, and 10% with IgG. Immunoglobulin infusions were well tolerated. Clinical and immunological investigations performed between the ages of 1 and 4 years showed no difference in growth rate, psychomotor development, susceptibility to infections and immune functions between children who had received immunoglobulin during the neonatal period and those who had not. After intravenous administration of immunoglobulins in high doses (12 g/24 h) to mothers 1 to 3 weeks before premature delivery (33 rd to 35 th week of gestation rise in serum IgG levels was observed in either mothers or children. Higher i.v. doses (120 g over 5 days) given between the 27 th and 32 nd weeks of gestation resulted in an increase of serum IgG levels in mothers but had no influence on serum IgG levels in their children.