Purpose: We evaluated the usefulness of Re-188 sulfur colloid for radiation synovectomy and therapy of intraperitoneal metastasis. Materials and Methods: We investigated the labeling efficiency of Re-188 sulfur colloid on various conditions. The stability of Re-188 sulfur colloid was observed at room temperature for 24 h and in human serum and synovial fluid for 72 h. The particle size distribution of Re-188 sulfur colloid was rneasured by filtering with various pore size filters. Animal experiment was performed in mice and rabbits. Results: The labeling efficiency of Re-188 sulfur colloid was 64,5+5.8% (n-5) at the conditions of sodium thiosulfate 40 mg, EDTA Nap.2HzO 0,8 mg, KReO< 0.8 mg at pH l. After purification, the radiochemical purity was higher than 99%. The stability of Re-188 sulfur colloid was high (>99%) at room temperature for 24 h and in human serum and synovial fluid for 72 h. The particle size distribution of Re-188 sulfur colloid was 0.3% (<1 pm), 11.2% (1-5 pm), 35.8% (5-10 pm) and 52.8% (>10 pm). In mice, 1 h postinjection of Re-188 sulfur colloid into tail vein, uptakes in lung, liver and muscle were 37.30-5.36, 32.33+5.79, 6.60+0.02% 1D/organ respectively. After I.p. injection in rnice, the uptakes of extraperitonial organs of Re-188 sulfur colloid at 1 and 24 h were 0.1+0.1, 0.4+0.1% ID/organ, and the excretions through urine and feces (-70 h) were low (2.68+0.80, 0.95+0.17%). When Re-188 sulfur colloid was injected to synovial space of rabbit, the uptake in other organs except knee was very low. Conclusion: Re-188 sulfur colloid showed high labeling efficiency, stability and potency for clinical use. (Korean J Nucl Med 1998;32:298-304).