Burn patients often exhibit prolonged cell-mediated immune suppression. Of the mechanisms proposed to account for this, one invokes an inability on the part of T lymphocytes to undergo blastogenesis, clonal expansion, and differentiation--a process partially mediated by interleukin-2. Triplicate samples of 10% dilutions of burn serum from nine burn patients (three with greater than 60% burn) were analyzed for their ability to suppress mitogen-induced lymphocyte blastogenesis. A separate aliquot of stimulated cultured lymphocytes was tagged with a monoclonal antibody to interleukin-2 receptors. The serum of patients with greater than 60% burn was significantly more suppressive (as measured by depressed tritiated thymidine incorporation by cultured lymphocytes) than that taken from patients with smaller burns. In addition, serum from those with larger burns caused a marked reduction in the interleukin-2 receptor-labeling index, suggesting that it possesses factor(s) that directly or indirectly block T lymphocyte interleukin-2 receptor expression.