We have evaluated in vitro cytotoxicity of cyanobacterial phycoerythrin (C-PE) on three human cell lines by cell proliferation and neutral red uptake assays. No toxic effects of C-PE were observed to any of the cell lines tested. The protective role of purified C-PE to potassium permanganate-mediated human fibroblast-DNA damage was assessed by comet assay at 0 (control), 10 and 20 microg C-PE ml(-1) doses in pre-, simultaneous and post-mutagen exposure conditions. Significant DNA damage was detected only in post-mutagen exposure conditions. Our findings confirmed that the C-PE is non-toxic and provides protection against permanganate-mediated DNA damage. The preliminary acute (2000 mg C-PE kg(-1) body weight, b.w.) and 90 day sub-chronic (0, 5, 15 and 25 mg C-PE kg(-1) b.w./day) oral toxicity studies of purified C-PE in male albino rats showed no mortality or treatment-related major clinical signs, and all the doses of C-PE were well tolerated. The no observed adverse effect level and no observed effect level were found to be 15 and 5 mg C-PE kg(-1) b.w./day respectively.