Laser induced fluorescence technique was used for detection of Lutetium Texaphyrin (Lutex) is vivo. Lutex is a new generation photosensitizer with rapid tissue clearance and deep red absorption characteristic. The detection system consisted of a nitrogen/dye laser (410 nm), an optical multichannel analyzer equipped with an intensified diode array, a specially designed fiber bundle, and a computer. Tissue fluorescence was first measured before injection of the Lutex to establish a baseline spectrum for each tissue. The fluorescence was then measured at 1, 2, 3, 4, 5, 6, 7, 8, 24, 48, 72 hours, 1, 2, 3, and 4 weeks after the injection. All spectra were normalized with respect to the total photon counts to determine the lineshape. The baseline was subtracted from all other fluorescence spectra. The Differential Spectrum showed a negative peak around 478 nm where the fluorescence of tissue was maximally absorbed by Lutex. Fluorescence was measured from mucus membrane of the lip, skin, and tumor in one case. Data for lip and tumor are presented here. As Lutex cleared the tissue, the negative peak at 478 nm approached zero. The clearance of the negative peak is presented for both lip (normal tissue) and nodular cutaneous metastatic breast is presented. In summary, absorption of tissue auto-fluorescence by Lutetium Texaphyrin may be used to detect the in vivo drug non-invasively. This technique may be used to determine the clearance of the Lutex in a variety of tissues.