The study aim was that of evaluate the effect of thymostimulin (Tp-1, Serono), either in vitro or in vivo, in patients with primary laryngeal carcinoma, treated only with surgery without any other complementary therapy. Nineteen patients have been studied: nine (mean age 62.5 years, range 48-70) have been treated with Tp-1 and ten patients (mean age 63.4 years, range 56-75) served as "controls". Tp-1 has been administered as follows: 60 mg/m2/daily i.m. days 1-15; 60 mg/m2 twice weekly i.m. days 16-30; 60 mg/m2 once weekly i.m. days 31-60. The treatment was stopped days 61-90. The same cycle was repeated until day 180. The treatment was stopped days 181-365. The following parameters have been assessed: clinical (at the protocol entry and after one year): Performance Status (PF, Karnofsky), local status, presence of relapses, incidence of chronic infections of the upper respiratory tract; immunological in vitro: 1) response to polyclonal mitogens, PHA, Con A and PWM, response to human recombinant Interleukin 2 (rIL 2) of PHA-prestimulated and non prestimulated peripheral blood lymphocytes. The immunological parameters also have been assessed at the protocol entry and after one year. Our results have shown that, in the group of patients treated with Tp-1, 5/9 patients (55.56%) exhibited a significant increase of the PHA response at the end of treatment as compared to pretreatment values, 3/9 (33.34%) showed a decrease and 1/9 (11.10%) an almost unchanged response. In the group of controls, 5/10 (50%) have shown a significant decrease of the response after one year, 3/10 (30%) an increase, 1/10 (10%) were unchanged and 1/10 (10%) exhibited a non univocal response.(ABSTRACT TRUNCATED AT 250 WORDS)