Postoperative changes in immunological parameters were examined in the patients with hepatocellular carcinoma, and the effect of the granulocyte protease inhibitor, ulinastatin, was investigated. Fifteen patients were divided into two groups randomly; eight patients were given 300,000 units of ulinastatin on the operative day and following seven days. The other seven patients who were not given it were regarded as the control group. The following parameters were examined; natural killer (NK) activity, lymphokine-activated killer (LAK) activity, and interleukin-2 (IL-2) producing activity. NK activities were decreased below normal limit at 1, 3, and 7 postoperative days (POD) in the control group. In the ulinastatin group, NK activity at 1 POD was decreased below normal limit, but this was increased from 3 POD and reached the preoperative level at 7 POD, which was significantly higher than that in the control group (p < 0.05). Also decrease of IL-2 producing activity at 7 POD was observed in the control group. But this change was inhibited in the ulinastatin group. These results suggest that the administration of ulinastatin improves anti-cancer immuno-reactivity in the postsurgical state.