We have studied 810 nm (Diomed, Cambridge England), 950 nm (Diolase, Endocare, Irvine CA), 980 nm (Dornier, Munich Germany), and 1000 nm (Cynosure, Bedford MA) using free beam right angle firing fibers in the canine prostate. Because some lasers only accept specific fibers, and each wavelength has its own divergence properties, standardization of fiber and power density was not possible. Power was studied in increments to the maximum output for each laser. Laser-tissue interaction was studied by video endoscopy during lasing, pathology, and real time interstitial thermometry at 3, 7, and 11 mm deep from the prostatic urethra. We found that using the Dornier Sidefocus fiber at 25 W, 810 nm created a small vaporized cavity surrounded by a zone of necrosis, whereas 980 nm at 25 W caused more necrosis but little vaporization. Irradiation with 950 nm and the Prolase II fiber created deeper lesions at 40 W than 25 W. At 1000 nm with the angle delivery device produced by Cynosure, popcorn with the formation of carbonized cavities occurred at both 25 and 40 W. The lesions were only slightly deeper at the higher wattage. We conclude that the high power diode lasers are capable of producing volume lesions in the prostate. The different wavelengths, fibers and power densities lead to different laser-tissue interaction, and thus each wavelength needs to be considered separately.