Forty-three consecutive patients of venomous snakebite by the Japanese viper (Agkistrodon halys Blomhoffii, "Mamushi" in Japanese) were treated with an uniformly scheduled therapy from 1990 and 1994. The therapy was mainly composed of minimal dose of antivenin, methylprednisolon and cepharanthin. There were two clinical courses, i.e., the minimal envenomation course (Group A, n = 14) and the severe one (Group B, n = 29). Our treatment was so satisfactory that all patients of both groups fully recovered activities of daily living with neither organic disorders nor sequelae of the bitten extremities. The high appearance ratio of atypical lymphocytes (P < 0.05) and the increased ratio of lymphocyte count to White blood cell count (P < 0.02) could be indicators that predict which clinical courses the patients take.