A randomized, single-blind, placebo-controlled trial was carried out in 62 patients (30 with osteoarthritis of the hip, 32 with osteoarthritis of the knee) to examine the efficacy of glycosaminoglycan-peptide complex in the treatment of osteoarthritis. Patients received 8-week courses of trial medication, each consisting of intramuscular injections of 3 x 2 ml ampoules per week, alternating with 8-week periods free of trial medication, in addition to conventional drug therapy and physiotherapy, as required. After 2-years' treatment, glycosaminoglycan-peptide-treated patients showed significant improvements, as compared with placebo, in relation to night pain, pain during the day, joint mobility and walking ability. Similar results were seen with both osteoarthritis of the hip and knee. In osteoarthritis of the knee it was also possible to assess joint swelling and this also showed a significant improvement. There were no significant changes in range of joint movement except for a significant decrease in active flexion in the patients with osteoarthritis of the knee treated with placebo. In contrast with many anti-osteoarthritic drugs, glycosaminoglycan-peptide complex was very well tolerated. These results suggest that glycosaminoglycan-peptide complex may be a valuable alternative form of long-term therapy for patients with osteoarthritis.