The major cytotoxic activity of Moxa was extracted with CH2Cl2 and partially purified by three cycles of silica gel column chromatography. The active fractions showed higher cytotoxicity against six human tumor cell lines (two oral squamous cell carcinoma, one salivary gland tumor, one melanoma, two leukemia) than three normal oral human cells (gingival fibroblast, periodontal ligament fibroblast, pulp cell). All fractions failed to protect the cells from the cytopathic effect induced by HIV infection. ESR spectroscopy showed that all fractions produced little or no radical under alkaline conditions, while showing much lower O2- scavenging activity, generated by hypoxanthine-xanthine oxidase reaction, than antioxidants and polyphenols. Active fractions induced DNA fragmentation in HL-60 cells, but failed to modify the mobility and activity of mitochondrial Mn-containing superoxide dismutase (MnSOD), in contrast to Moxa smoke. These data suggest that the active principles in the Moxa extract might be different from that in Moxa smoke, which produced carbon radical and modified MnSOD mobility and activity.