Most preclinical and clinical studies involving Photodynamic Therapy (PDT) use continuous wave light generated from argon ion pumped dye lasers or appropriately filtered lamps in order to activate photosensitizers. Flashlamp pumped dye lasers and copper vapor pumped dye lasers can induce photon saturation effects which result in suboptimal photosensitization. As Photodynamic Therapy becomes more widely accepted by the medical community, the availability of a specialized, low maintenance, high efficiency laser to the clinician has become an important issue. With an appropriate system reduced treatment time may be achieved through higher laser power output and the use of fiber splitters. In a study by Ferrario et al.,1 a quazi-continuous wave laser which couples a pulsed 532nm potassium titanyl phosphate (KTP) [Laserscope, San Jose] laser to a flow dye cell laser tuned to 630nm (PDT Systems 630) [PDT Systems, Santa Barbara] was evaluated in a variety of in-vitro and in-vivo PDT experiments. It was found that comparable results to those in argon ion laser studies were obtained in all experiments. In order to determine if these findings would translate to the clinical setting, an addendum was attached to an ongoing IRB approved study utilizing Photodynamic Therapy for the treatment of nonmelanoma skin cancer at the Western Institute for Laser Treatment. The purpose of this study was to further compare KTP pumped dye laser versus argon pumped dye laser systems utilizing the photosensitizer, Photofrin' 1 mg/kg in a series of skin cancer patients. PDT was offered as a potentially curative treatment for those patients with small, local lesions while being offered as a palliative modality for those patients with metastatic disease. 48 hours postinjection of photosensitizer, and after fluorescence detection in known and suspected tumor sites utilizing a krypton laser emitting at 408nm, the treatment areas were delineated. 630 +1 3nm of laser light (CW from an argon pumped dye laser and pulsed light from a KTP pumped dye laser) was delivered utilizing a flexible 400p. quartz forward surface microlens to the tumors. A total of 1 6 treatment sites were compared in a side by side fashion. Dosimetry factors including Total Dose, Dose Rate and lesional geometry were identical in sites compared. Tumors treated included metastatic breast adenocarcinoma, squamous cell carcinoma, basal cell carcinoma and Kaposi's sarcoma. The patients were followed up at 24 hrs., one week, four weeks, eight weeks, twelve weeks, and quarterly thereafter. Treatment selectivity, lesion response, and normal skin response were graded and recorded including photodocumentation. The conclusion drawn from our work was that in all parameters evaluated the results proved equivalent. There were no clinical differences in those patients treated with argon continuous wave or KTPpulsed dye laser systems. Subsequently a series of patients were treated with the KTP pumped laser system alone. Facilitated by the reliable delivery of 35 watts of 630nm light and the use of fiber splitters, three treatment areas could be illuminated at one time, reducing treatment time to one third of that of the argon pumped dye system.