We showed that PC12 cells and 3T3 cells cultured in dishes were killed by illumination with visible white light from a halogen lamp at 7 x 10(4) lx for 5 min in the presence of either 10 mu M hematoporphyrin or 2 mu M methylene blue as a photosensitizer. This simple technique, based on the photodynamic reaction via generation of reactive oxygen species can be applicable for patterning cultured cells.