Asplenia syndrome is usually associated with complex congenital cardiovascular defects. These patients often succumb to overwhelming infections. A complete immunological evaluation was therefore conducted on 13 consecutive patients with asplenia syndrome and 12 age-matched patients with congenital heart disease but without evident splenic problems. IgG, IgA, IgM and C3 and C4 values were normal for age in all subjects studied. T cell subsets, including the percentage of CD3, and CD4 cells and the CD4/CD8 ratio were significantly different in patients and controls (P less than 0.01, respectively). Lymphoproliferative responses to mitogens (ConA, concanavalin A, phytohemagglutinin and pokeweed mitogen) were also decreased in patients. Fc-mediated clearance of sensitized autologous erythrocytes was significantly impaired in patients (n = 13) when compared with age-matched controls (n = 5) (clearance t1/2 59.0 +/- 9.6 minutes vs. 12.5 +/- 1.6 minutes, P less than 0.001). Thus profoundly impaired reticuloendothelial clearance and decreased T cell function might account for the life-threatening infections frequently seen in patients with congenital asplenia syndrome.