The effect of methamphetamine on the pulmonary metastasis was investigated in C57BL/6 mice injected with Bl6 melanoma cells. Bl6 melanoma cells (2$ imes$10$^{5}$ cells) were injected intravenously into 5~7 weeks old C57BL/6 mice. Mice were then treated intraperitoneally with methamphetamine either acutely (two times with one week interval) or subchronically (daily for 14 days). Degree of pulmonary metastasis was investigated and specific immunologic parameters such as natural killer cell cytotoxicity(NKCC), antibody-dependent cellular cytotoxicity(ADCC) and blastogenic responses of splenocytes were examined. Mice which had been subchronically treated with methamphetamine showed significant decreases in the number of pulmonary metastasis of Bl6 melanoma cells, NKCC and ADCC without a significant change in blastogenic responses. In the acutely-treated group, slight trends of decrease in the numbers of pulmonary metastasis, NKCC and ADCC were observed without statistical significances whereas there was a significant increase in blastogenic responses. The mechanism underlying the decrease in the degree of metastasis despite diminished NKCC and ADCC after methamphetamine treatment and the relationship between the degree of pulmonary metastasis and duration of methamphetamine treatment remain to be investigated.