Skin biopsies from 30 renal transplant patients were investigated for cellular infiltrates and deposits of IgM, IgA, IgG, C3, and C5-9 neoantigen. Granular perivascular deposits of IgM were detected in biopsies of 8 of 14 patients during active cytomegalovirus (CMV) infections and in none of 16 controls. In 5 biopsies, the IgM deposits were accompanied by little or no IgG, IgA, or C, while in 3 biopsies definite C3 deposits were present. One of the biopsies with C3 deposits also had C5-9 deposits and another had C5-9 and IgA deposits. Three monoclonal antibodies failed to detect early or late nuclear antigens of CMV in the deposits. These deposits were not associated with clinically evident manifestations of vasculitis. A strong correlation was found between IgM deposits in the skin and IgM circulating immune complexes (CIC) and also IgM rheumatoid factor (RF). The deposition of IgM was not more frequent in primary than in secondary CMV infections, and it did not correlate with the production of IgM antibodies that were specific for CMV antigens.