Glucosamine sulfate (Dona, CAS 29031-19-4) is a drug used in the treatment of osteoarthritis. When orally given, it is more effective than placebo and at least as effective as non-steroidal anti-inflammatory drugs in relieving osteoarthritis symptoms. The aim of this multicentre, randomised, placebo-controlled, double-blind, parallel-group study was to assess the efficacy and safety of glucosamine sulfate intramuscularly given on the same parameters. 155 out-patients with knee osteoarthritis (Lequesne's criteria), radiological stage between I and III, Lequesne's severity index of at least 4 points and symptoms for at least 6 months, were treated with i.m. glucosamine sulfate (or placebo) 400 mg twice a week for 6 weeks. Clinic visits were performed at enrollment, after a 2-week baseline, at weekly intervals during treatment and 2 weeks after drug discontinuation. Responders to treatment were considered those patients with a reduction of at least 3 points in the Lequesne index, together with a positive overall judgement by the investigator. The Lequesne index was slightly over 10 points in average in both groups at the beginning of treatment. A significant decrease in the index was observed for glucosamine compared to placebo (3.3 vs. 2.0 points in average, respectively; p < 0.05, Student's t-test). The responder rate in the evaluable patients was 55% with glucosamine (n = 73) and only 33% (n = 69) with placebo (p = 0.012, Fisher's Exact Test). According to the intention-to-treat approach, considering also drop-outs, these proportions were 51% vs. 30% (p = 0.015).(ABSTRACT TRUNCATED AT 250 WORDS)