Abstract: The effect of howiinol A (GHM-10) on the growth of several cancer and normal cells were studied, using the methods of cell growth curve determination, MTT test and soft-agar colony formation assay. The results showed that GHM-10 exhibited potent inhibitory effect on cancer cells with an IC₅₀ of 2 μg·ml^-1 approximately. Normal cells, especially bone marrow progenitor cells, were shown to be less sensitive to GHM-10. A drugresistant cell line, KB/VCR200, was found to be as sensitive as its parental KB cells. GHM-10 did not induce HL-60 cell differentiation. In murine transplantable tumors, GHM-10 was found to have significant therapeutic effect on mice bearing solid tumor hepatoma H22, Lewis lung carcinoma and S180 ascites.