Objective: To evaluate the effects of low-intensity ultrasound (LIUS) stimulation on the anabolic state of human cartilage from patients with osteoarthritis (OA). Methods: Explant cultures of human OA cartilage were stimulated for 10 min every day for 7 consecutive days using continuous-wave sonication at a frequency of 1 MHz with spatial and temporal average intensities of 0 (control), 40, 200, 500, or 700 mW cm2. The effects of LIUS on cell proliferation were evaluated by 3H-thymidine incorporation. Proteoglycan synthesis was evaluated by the incorporation of 35S-sulfate and by Safaranin O staining. Collagen synthesis was evaluated by 3H-proline incorporation and immunohistochemistry. Results: At an intensity of 200 mW cm2, LIUS treatment induced the expression of collagen type II and proteoglycan measured by the incorporation of radioactivity and specific staining of the cartilage explants. However, the expression decreased again at the higher intensities of 500 or 700 mW cm2. Ultrasound had no stimulatory effect on cell proliferation at any intensity. Conclusion: LIUS has anabolic effects on human cartilage in explant cultures, indicating a potentially important method for the repair of osteoarthritic cartilage.