Zn(II)PPIX exerts cystostatic/cytotoxic effects against tumor cells. Tumor cells were incubated with serial dilutions of Zn(II)PPIX for 48 or 72 hours. The cytostatic and/or cytotoxic effects of treatment were measured with a standard crystal violet staining assay. Bars represent means ± SD. *P < 0.05 (two way Student's t-test) in comparison with controls.