Splenectomy has been reported to alter inconsistently the CD4 lymphocyte numbers in patients infected with the human immunodeficiency virus (HIV). To further assess the effect of splenectomy we have retrospectively examined the charts of 10 patients who were infected with HIV and who had undergone splenectomy. There was a significant increase in the mean CD4 numbers following splenectomy (mean increase of 326/microliters, or 2.1-fold, P = 0.0009), the total lymphocyte numbers (mean increase of 1.55/ml, or 2.2-fold, P = 0.001) and in the CD8 lymphocyte count (mean increase of 968/microliters, or 2.3-fold, P = 0.014). No significant difference was observed in the percentage CD4 lymphocytes (P = 0.95) or in the CD4:CD8 lymphocyte ratio (P = 0.76). In two patients, symptoms suggestive of impaired immune function developed post-splenectomy, at a time when their CD4 lymphocyte numbers were markedly higher than their pre-splenectomy values. One developed oral candidiasis (CD4 960/microliters, percentage CD4 32%), and in one patient a 7 kg weight loss was associated with recurrent mouth ulcers (CD4 680/microliters, percentage CD4 7%). We conclude that the total CD4 count increases significantly after splenectomy while the percentage CD4 lymphocyte count and CD4:CD8 lymphocyte ratio do not. Our data suggest that the CD4 lymphocyte count overestimates the immune function in these patients, although our findings are not conclusive.