In studies with normal and rheumatoid synovial fibroblast cultures the effects of sodium aurothiomalate on the quantity and quality of hyaluronic acid were tested. This gold compound produced one clear effect: the molecular weight of hyaluronate produced by rheumatoid fibroblasts was increased (shifted towards normal) whereas the effects on the amounts of hyaluronic acid synthesized were small in both rheumatoid and control cultures. The importance of this finding in relation to the known beneficial effects of gold preparations in clinical medicine is discussed.