The dynamics of synthesis and accumulation of protoporphyrin IX induced by 5-aminolevulinic acid (5-ALA) was studied using confocal fluorescence microscopy in three established cell lines: immortalized cells originated from human tumor tissues-epithelial carcinoma (HeLa cells) and lung adenocarcinoma (A549 cells)-and immortalized fibroblast-like mouse embryo cells (3T3 line). The accumulation of protoporphyrin IX in cell cultures was estimated by analyzing the intensity of its fluorescence. The dynamics of changes in the fluorescence intensity with the cell incubation duration in the presence of 5-ALA and with the 5-ALA concentration was studied.