Immunoglobulins A, G, and M to cytomegalovirus during recurrent infection in recipients of allogeneic bone marrow transplantation. Occurrence and significance of specific IgA and IgM to cytomegalovirus (CMV) in recurrent CMV infection was evaluated in 21 allogeneic T lymphocyte-depleted bone marrow transplantation (BMT) recipients who had been previously CMV seropositive. Of 17 patients with CMV infection, viruria was detected in 94%, CMV-specific IgA in 88% and IgM in 76%, and a fourfold rise in IgG in 65%. The median time between BMT and detection of viruria was 69 days, of IgA 70, of IgM 62, and of IgG 88 days. The IgM and IgA responses lasted for 14 and 30 days (median time), whereas high IgG titers persisted. Twelve patients developed CMV disease; in these the appearance of viruria, IgA, and IgM preceded the rise of IgG (P less than .02). CMV-specific IgA and IgM are valuable diagnostic tools in BMT recipients with recurrent CMV infection. 