Forty-nine patients diagnosed as having gonarthrosis were given intra-articular treatment with hyaluronic acid (Adant or Hyalgan) in a blind randomised study. We concluded that the efficacy with Adant at 3 months after treatment was greater than with Hyalgan (50% versus 21.1%). The maximum improvement with hyaluronic acid was seen at 5 weeks in 75.4% and the adverse effects consisted of pain in the infiltration side which was almost twice as great with Adant (16.3%).