Comparisons are made between a large group of mongols cared for in institutions and their carefully matched controls in respect of (a) serum levels of immuno-γ-globulin (γA, γG, and γM) and (b) the incidence of pyrexial illnesses over a retrospective five-year period. Male mongols are found to have higher levels of γA-globulin than their male controls and a higher incidence of pyrexial illnesses. Otherwise no significant differences were found. The findings are discussed in the light of previous studies.