Meniscal tears and partial thickness defects in articular cartilage do not heal spontaneously. In this paper results are described of studies of a procedure for evoking the healing response in such lesions by a non-thermal tissue sparing photochemical weld using 1,8-naphthalimide dyes. Fifteen essentially mature Barbados sheep 40 - 60 pounds in weight received a 2 - 3 mm flap tear by incision in the red white zone of the medial meniscus oriented parallel to the table of the tibia. The animals were divided into four groups; Group I, no treatment; Group II, treatment by laser activated photoactive dyes; Group III, treatment by suturing; Group IV, treatment by laser irradiation only; Group V, treatment by photoactive dyes only. In another group of 12 sheep partial thickness flap tear was created by incision in the articular cartilage of the femoral condyle. These were divided into four groups as for the meniscus study, omitting the sutured control. Welds were made using the dimeric dye MBM Gold BW 012-012-012 at 12 mM in PBS, 457.9 nm argon ion laser radiation at 800 mW/cm2, 7.5 minutes (360 J/cm2) with approximately 2 kg/cm2 externally applied pressure. Animals were sacrificed at 24 hr, 4 weeks, 3 and 6 months postoperatively. Gross appearance of menisci and cartilage in all welded knees was normal and all welds resisted deformation or loosening under forceful probing. Histology of studies of both tissues out to 6 moths disclosed close bonding of welded area, continuing healing response in the form of cellular recruitment and protein deposition and the absence of inflammatory response. Tissue erosion and arthritic changes were evident in all unwelded controls.