Averaged absorption spectra from 13 tumors in 12 patients aged from 30 to 39 years. The tumor spectra clearly demonstrate different spectral features from the normal tissue. The increased absorption in the 650 to 850 nm region is indicative of increased oxy- and deoxy-hemoglobin concentration. The increased absorption in the 950 to 1,000 nm region is indicative of increased tissue water concentration. Normal tissue lipid contrast is evident in the 900 to 950 nm region (Tables 1 and 2). Error bars represent the standard error of the mean for the given population, shown every 20 nm.