Protoporphyrin IX (PPIX) fluorescence-guided brain tumor resection using 5-aminolevulinic acid labeling is one of the most valuable tools available to determine the extent of glioma infiltration, but requires repeated spectroscopic evaluation of the tissue. The present method informs the surgeon of residual tumor in real time using spectrum analysis of PPIX fluorescence and an audible alert system. The target region was illuminated with a laser with a peak wavelength of 405 +/- 1 nm in addition to the usual microscope halogen lamp during tumor resection. Analysis of the spectrum detected the PPIX peak using a difference in relative intensity exceeding 500 at 636 nm and 632 nm, when an audible alert was transmitted to the surgeon. Using this method, infiltration of glioma was detected and confirmed histologically in three of six glioblastomas. The surgeon can detect tumor infiltration far more objectively and with less effort using this system during tumor resection.