The Neodynium: Yttrium Aluminum Garnet (Nd: YAG) laser was one ofthe first lasers to allow tissue photoablation to be performed transendoscopically in the standing equine patient.1 It became very popular due to the fact that its irradiation can be applied through flexible fiber optic cables. Recently, a number of diode lasers have been marketed to the equine practitioner as replacements for the Nd: YAG laser, specifically the 810nm and 980nm diode lasers. Initially, both of these lasers produced a maximum of 20 watts total power output. Currently, higher power output versions being 50 or 60 watts are available to the practitioner. Producing a high power output means these lasers have the potential to be used in the non-contact configuration, as well as contact, when performing corrections of upper respiratory disorders ofthe horse. Penetration studies have been performed using lower power (20 watt) 810nm and 980nm diode laser which were compared to the depths and widths of penetration produced by the Nd: YAG laser.2,3 The purpose of this investigation was to evaluate the 60 watt 810nm diode lasers penetration delivering 200-600 joules on to equine respiratory tissue. Penetration parameters selected were width and depth of craters and were compared to the Nd: YAG laser set to deliver 200 joules of energy. This study determined that the 810nm diode lasers penetration parameter is close to that of the Nd: YAG laser. As the diode laser power output increased above 200 joules, it significantly penetrated respiratory tissue deeper than the Nd: YAG laser set at 200 joules output. Measurement of the crater depth created by the 810nm diode laser as its output power was increased at 100 joule increments was significantly deeper than the depth of crater formed by the previous power setting. Similarly, the diode laser's crater top and bottom width measurement, at 400 joules and greater, was significantly greater than or equal to that of the Nd: YAG lasers set to deliver 200 joules of energy. This investigation provided evidence that the 60 watt 810nm diode laser produces substantial penetration that can be applied not only in the contact mode successfully, but also in the non-contact mode providing the practitioner with a more versatile laser for transendoscopic application in the equine.