The immunogenicity of a sodium hyaluronate preparation for clinical use (Healon, Healonid, Pharmacia AB, Sweden) in ophthalmology and certain joint diseases has been tested in man. For immunization, two subcutaneous injections of 10 mg of sodium hyaluronate were given at an interval of 1 week. The following criteria were used as indicators of immunogenicity: skin prick test, microprecipitation test and complement analyses. No evidence for immunogenic properties was obtained in any of these tests. This refers to sodium hyaluronate itself and to the trace amounts of protein components contained in the preparation.