The purpose of this study was to estimate the efficacy of an endogenous sensitizer (delta-aminolevulinic acid (or ALA) induced protoporphyrin IX (or PpIX)) and an exogenous sensitizer (meta(tetrahydroxyphenyl)chlorin or m-THPC) on two different cell lines, rat colon adenocarcinoma PROb cells and murine melanoma B16A45 (B16) cells, in apoptosis production. After sensitizer incubation, cells were irradiated with an argon dye laser. LD(50) with m-THPC was 2.8 microg/ml and 4.7 microg/ml under irradiation of 25 J/cm(2) respectively for PROb and B16 cells. With ALA, LD(50) was 150 microg/ml and 175 microg/ml under 25 J/cm(2) respectively for PROb and B16 cells. Apoptosis induction by m-THPC or ALA-PDT was detected by DNA gel electrophoresis and quantified using an ELISA assay 24 h after PDT. The maximal apoptosis enrichment factor (MAEF) was reached for 6 microg/ml m-THPC at 10 J/cm(2) for PROb and B16 cells and for 50 microg/ml ALA at 25 J/cm(2) for PROb or B16 cells. Both m-THPC and PpIX are efficient photosensitizers and apoptosis inducers. However, MAEF is obtained by sensitizer or laser doses inducing very different phototoxic effects: MAEF was obtained after m-THPC-PDT with LD(78) for PROb cells and LD(30) for B16 cells and after ALA-PDT with LD(22) for PROb cells and LD(18) for B16 cells. However the overall m-THPC/PDT apoptotic induction (under the curve surface analysis) was not different whatever the cell line for 10 and 25 J/cm(2). On the contrary, ALA-PpIX/PDT apoptotic induction was twice for 25 J/cm(2) as compared to 50 J/cm(2) (p < 0.01) for both the PROb and B16 cells. These results indicate that the apoptosis rate in PDT cell killing varies considerably according to cell type and sensitizer.