The use of near-infrared (NIR)–excited Fourier-transform (FT) Raman spectroscopy as a technique for evaluating the extent of photosensitizer localization in tumor (human pancreatic adenocarcinomas)–bearing mice has been tested using lutetium(III) texaphyrin analogue Lu-T₂B₂Tex. The complex was injected subcutaneously in the form of three injections given during the course of 3 days. The kinetics of biodistribution were then followed over a time scale of 1–6 days. The NIR-FT-Raman spectra of tissue samples obtained from the xenographic tumor, muscle, heart, brain, liver, spleen, kidney and blood were recorded and used to identify the presence of Lu-T₂B₂Tex in these tissues. Five Raman sensitizer markers were used to estimate the relative content of Lu-T₂B₂Tex in tumor at various postinjection times. UV–Visible (Vis) absorption spectroscopic detection of this sensitizer in tissue extracts was applied as a conventional method. Both spectroscopic methods were in good agreement with each other and confirm that Lu-T₂B₂Tex localizes well in tumor tissue. Maximal drug content was observed 3 days after the final injection. This time delay seems to be optimal for tumor irradiation in photodynamic therapy.