A 3-year-old male with inflammatory bowel disease and hypogammaglobulinemia was found to have decreased T lymphocyte function. His serum was shown to depress normal T cell proliferative responses to phytohemagglutinin. Incorporation of lithium chloride to in vitro cultures enhanced autologous lymphocyte responses to phytohemagglutinin. Since lithium acts by inhibiting cAMP production, the child's lymphocytes were postulated to have increased levels of cAMP. Both lymphocytes and serum were shown to contain elevated levels of cAMP. In vivo therapy with lithium citrate was initiated and enhanced T cell numbers and function were observed concomitantly. Serum cAMP was also reduced to normal levels. The patient showed initially marked clinical improvement as assessed by mood, weight gain, and diminution of diarrhea. This clinical improvement was unfortunately not sustained despite the continued improvement in immune parameters and cAMP levels.