The most important sequelae of splenectomy is immunity depression. This study, conducted in three phases, was aimed at confirming this clinical condition. Data from our phase 1 study clearly show that patients undergoing splenectomy for trauma are in a critical condition because of a latent immunodeficiency shown by skin tests (ST) and in vitro evaluation of the aspecific immune activity. Because the in vitro study of the unspecific immunity that we used seems to be more expensive and complicated than ST, the aim of the phase 2 study was to compare the efficacy and the limits of the two assays (ST versus in vitro study) in detecting the immunodeficiency status of the splenectomized patient. The aim of the phase 3 study was to ascertain whether postsplenectomy immunodeficiency could be a consequence of an altered equilibrium between the lymphocyte subpopulations T helper (Th)1/Th2, evaluated by serum dosage of interferon-gamma and interleukin-4.