Total serum IgA and IgA antibodies to some milk antigens are often associated with severe atherosclerosis. In the present study we examined the same serum samples to evaluate the possible involvement of serum IgA antibodies to apoproteins and lipoproteins and their relationship to IgA antibodies to milk antigens. We studied 23 subjects with angiographically assessed atherosclerotic lesions (ATS group) and 20 healthy control subjects with a similar age range (59-69 years) and sex distribution. Anti-ApoB, Apo A-I, Apo A-II and anti-LDL, VLDL and HDL antibodies were measured with the ELISA method. All antibodies tested except those to anti-Apo A-I were significantly higher in the ATS group with respect to controls with a maximum significance for anti-Apo B IgA (p = 0.0018). When, for each antibody, a threshold of positivity was set to the mean + 2 SD of values in the control group, 12 ATS subjects (52%) and 1 control (5%) were found to be positive for either anti-Apo B or anti-Apo A-II IgA. Most of the correlations of anti-apoprotein and anti-lipoprotein IgA with anti-milk protein IgA and total IgA were significant. The association of these antibodies with atherosclerosis might either be specific or represent part of a polyclonal IgA response. Whether this association is a cause or an effect of atherosclerotic disease is presently unknown.