Time-lapse analysis of phase shift using phase-shifting laser microscopy (PLM) revealed that the laser phase shifts of primary normal human prostate epithelial cells (PRECs) and human prostatic carcinoma epithelial cell line (PC-3) cells during the mitotic phase were markedly higher than those in the interphase. The phase shift of PC-3 cells during the interphase was markedly lower than that of PRECs throughout the cell cycle. In conclusion, it was proposed that adherent PC-3 cancer cells could be noninvasively discriminated from normal adherent PRECs by the periodical measurement of phase shift using PLM during culture. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.