Colloidal gold ¹⁹⁸Au were injected into 40 knee joints of rabbits for the study of the change of synovial membrane. We verified even distribution of Colloidal gold ¹⁹⁸Au about knee joints by use of scintigraphy. After then, histopathological examinations were performed by periodic intervals. The following results are obtained form this study. l. Intra-articular injection of Colloidal gold ¹⁹⁸Au into rabbit's knee joints resulted in a mild resctive inflammation at synovium. In was charscterized by an infiltration of eosinophils and by sclerotic changes in the subsynovium and by fibrosis of synovial vessels. 2. From this study, intra-articular injection of Colloidal gold ¹⁹⁸Au may by benefit to treat the chronic synovial effusion in human.