The Authors evaluated the efficacy of thymopentin in the prevention of post-splenectomy infections. 14 splenectomized patients treated by thymopentin (50 mg s.c. every other day in the 4 weeks following splenectomy) were compared with 14 splenectomized control patients. Clinical evaluations and measurement of CD4 and CD8 lymphocyte subpopulations were made preoperatively and then after 3 and 6 months from splenectomy. Hyperthermia (37.5-38 degrees C) "sine materia", which disappeared spontaneously in 4-5 weeks, was observed in the post-operative phase in 4 control patients and in 1 patient treated by thymopentin. No statistical difference was demonstrated comparing pre- and post-operative percentages of CD4 and CD8 lymphocytes in the treated and control groups.