The noninvasive discrimination of cancer cells from normal cells in adherent culture by the measuring of the phase shift using phase-shifting laser microscopy (PLM) was investigated with the aim of noninvasive quality control of cell processing for transplantation. A human prostatic carcinoma epithelial cell line (PC-3) and human hepatocellular carcinoma cell lines (Hep3B, PLC, HLF, and Huh7) showed markedly lower phase shifts as measured by PLM than those of human prostate epithelial cells (PREC) and cryopreserved human hepatocytes, respectively, although there was no apparent difference in cell morphology between these sets of cells. Mixed cultures of PC-3 and PREC, in which the percentages of PC-3 cells were determined to be 43.3%, 14.0%, and 10.6% by immunofluorescence staining, were prepared, and the percentages were calculated to be 50.0%, 8.0%, and 2.5% using the distribution of the phase shift data of the cells, respectively. In conclusion, these adherent cancer cells can be noninvasively discriminated from normal adherent cells by phase shift measurement using PLM, and the sensitivity of the method of detecting cancer cell contamination reached 10%. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.