Immunoglobulins (IgG; IgM, IgA, IgD, and IgE) in serum were measured in three age groups of Negroid people: 5–9 years, 10–14 years, and adult in St. Lucia and St. Vincent and 10–14 years in Cleveland. The St. Lucians and St. Vincentians are comparable populations of Caribbean islands 30 miles apart. All the St. Lucians in the study were infected with schistosomiasis and many had other intestinal parasites; none from St. Vincent had schistosomiasis but many had intestinal parasites. Those in Cleveland had neither schistosomiasis nor any intestinal helminthic infections. The St. Lucians had a significantly higher level of IgG in all age groups and a higher level of IgM in the age group 5–9 years; both of these differences have been reported in other populations but without adequately matched control groups. There were no striking differences in the mean concentrations of IgA and IgD. IgE levels were markedly higher in both island groups than in the Cleveland group, but since the mean values were similar for younger and older children, this difference cannot be attributed primarily to schistosomiasis. The mean IgE level of the St. Lucian adults was more than fivefold higher than that of the St. Vincentians; this difference might be attributable to schistosomiasis.