In the present paper we address the question if fluorescence diagnostics can be used to monitor and possibly predict the outcome of photodynamic therapy (PDT) using the tumor seeking agents Photofrin and (delta) -aminolevulinic acid (ALA). The degree of selective uptake may vary from patient to patient and it would be interesting to use the drug-related fluorescence signal as a tool to tailor the treatment strategy. Clearly, the fluorescence intensity cannot be directly related to the tissue drug contents because of varying absorption and scattering properties of the tissue. However, because of the real-time capability of fluorescence it is interesting to see how far the fluorescence information can be utilized for optimizing the light delivery. Patients with basal cell carcinoma and spread metastatic breast cancer in the skin were treated. Two different doses, 1 and 2 mg/kg b.w. of Photofrin (Quadra Logic, Vancouver, Canada) were used. The treatment laser was a Nd:YAG pumped dye laser (Multilase Dye 600, Technomed International, Paris/Bron, France). The system provides 1064 nm IR and 532 nm green light from the Nd:YAG laser as well as red light in the region 620 - 670 nm from a dye laser. The treatment procedure was preceded by fluorescence measurements for allowing comparisons between the diagnostic signals and the treatment outcome. At the end of the treatment, fluorescence was again monitored to assess the degree of bleaching manifested by the appearance of an additional red peak. Our data on the connection between fluorescence signals, delivered dose and observed treatment outcome are presented and the potential of imaging fluorescence monitoring in PDT dosimetry is discussed.