The CO2 laser is a precision surgical laser because of its high degree of absorption in soft tissue with limited lateral damage. The tissue, which absorbs the CO2 laser energy, and has a high water content, will be converted to vapor with a small residue of ash and a by-product of heat. The laser can only be effective if these by-products, i.e. vapors, heat, and carbon ash residue, are not injurious and are well tolerated by the joint. These by-products must be either reabsorbed by the synovium or remain as a nonviable substance in the joint. From April 1989 through April 1990, 40 patients underwent 43 operative arthroscopies of the knee using the Pfizer CO2 laser. All procedures were chondroplasties, synovectomies, and/or meniscectomies. All accessible CO2 carbon ash residue was removed from the joint after the procedures using an intraarticular shaver and hand rasp. Postoperatively there were no cases of hemorrhagic effusions, subcutaneous emphysema, or synovitis. Histologic examinations performed on 10 patients undergoing subsequent surgery showed no evidence of carbon ash residue or synovitis seen grossly or microscopically. The carbon ash residue is not noxious to the joint and is completely removed from the joint, presumably by the synovial response.