Visualization of regent-dose effects on human prostate cancer cells in photodynamic therapy (PDT) was tried by microscopic laser speckle observations. The used regent was 5-aminolevulinic acid (5-ALA), which induces protoporphyrin-IX to give photodynamic damages to cells with 635 nm laser illumination. By analyzing frequency spectra of laser speckle fluctuation (LSF) observed on cells in PDT, it suggested that LSFs at cellular membranes and inside cells indicate different behavior each other. (C) 2010 Optical Society of America