Effects of prostaglandin E1 on collagen diseases with high levels of circulating immune complexes. Prostaglandin E1 (PGE1) was administered to 4 patients with collagen diseases presenting with high levels of circulating immune complexes (CIC) in sera. Our study patients had progressive systemic sclerosis, systemic lupus erythematosus, polyarteritis nodosa, and rheumatoid arthritis. In all 4 patients, CIC levels significantly decreased after administration of PGE1 by continuous infusion at 10/ng/kg/min via central venous catheter for 72 h. In addition, the skin ulcer in a patient with PSS healed completely, and the finger necrosis in a patient with RA improved. These results suggest that PGE1 given by continuous venous infusion is effective in reducing CIC, in addition to improving peripheral vascular disorders. 