Immunological abnormalities of 163 IgA-deficient blood donors were studied. Anti-IgA antibodies were found in 15, anti-IgG antibodies (measured by the Ripley test) in 34, latex test positivity in 21, anti-IgM antibodies in 9 and antibodies against bovine milk in 41 sera. These numbers differed significantly from the control groups of normal blood donors. In the studies of thyroglobulin antibodies, antinuclear antibodies and blood group A and B isoagglutinins there was no difference from the controls. Interrelationships of all findings were studies by statistical analysis. Correlations were found between latex and Ripley tests and rheumatic disorders as well as between high age and anti-IgA antibodies. Male subjects had antibodies against bovine milk more often than females. Otherwise no striking findings were brought up by the statistical analysis.