A group of mice implanted with squamous cell carcinoma (CAl025) and melanoma (B16) were irradiated with a cw krypton laser using 3374A degree (total dosage 346 j/cm**2, and 660 j/cm**2), and 3507A degree (total dosage 367 j/cm**2), and a pulse N//2 laser using 3371A degree (total dosage 471 j/cm**2, 660 j/cm**2, and 165 j/cm**2). In all groups, tumorous mice were used as controls. Regression of tumors was observed at wavelengths of 3374A degree and 3371A degree (total dosage 471 j/cm**2 and 660 j/cm**2). No regression was observed at 3507A degree . The regression in some cases was very impressive. The preliminary work on N//2 laser irradiation of basal cell carcinoma (in human beings) and of BEL 7404 liver carcinoma cells in vitro and irradiation of one patient with an N//2 laser performed in China are also reported.