In order to investigate the preventive and therapeutic effects of Herba Houttuyniae, experimental studies on the immune response and histological findings were undertaken. The results of these studies were summarized as follows; Delayed type hypersensitivity and rosette formation rate were significantly increased compared with control group. Hemagglutination, hemolysin titer and NK cell activity were variable, not significantly against the control group. When observed on lung tissue recovery; experimental groups were shown to be significantly recovered as compared with the control group. From these results, it is suggested that Houttuyniae Herba promotes immune response and reduces the recovery time of pneumonitis and lung abscess from the histological viewpoint.