Forty-one patients with Hodgkin's disease staged as IA(4), IIA/B(4/6) IIIA/B(6/9) and IVA/B(3/9) who had had radiotherapy (subtotal nodal irradiation (STNI) or total nodal irradiation (TNI), or combined one (STNI/TNI plus chemotherapy MOPP or MOPP/ABVD) have been enrolled consequently and randomized to receive thymic hormone (17 patients) or pentapeptide treatment (14 patients) for 3-6 months at the end of the therapeutic regimens. In all patients severe immunodeficiency evaluated either as leukopenia (WBC less than 4000/mm3) or lymphocytopenia (lymphocytes less than 1500/mm3) or CD3 and CD2 cell reduction, or imbalance of helper/suppressor (H/S) ratio have been documented before starting thymic therapy. Different results by immunorestorative therapy have been registered according to the entity of immunodeficiency. In fact in the group of 15 patients with severe lymphopenia (lymphocytes less than 1000/mm3) either the thymic hormone or the synthetic drug produced a significant increase of all subsets examined: CD3-CD2-CD4-CD8 without or with minimal influence on H/S ratio, due to the increase of absolute lymphocytes count. In the remaining patients with mild or no lymphopenia the two drugs resulted ineffective on T cells. Comparing the overall group of patients who received thymic therapy with a control group of patients who did not, an advantage in terms of recruitment of T cell compartment has been observed in the former group when mean values are compared. According to the clinical impact of the immunotherapy with thymic substances on these patients, a significant decrease in incidence of herpes virus infection (HVI) has been observed in patients who had had thymic therapy compared with the incidence of HVI in the control group (18% versus 53.8%).(ABSTRACT TRUNCATED AT 250 WORDS)