Abstract: It has been newly found out that ascochlorin, which is a publicly known fat-soluble antibiotic, and its homologues serve as a ligand of retinoid X receptor and react in vivo with the amino group of serum protein to form Schiff bases without showing any side effect of retinoid. Ascochlorin and its homologues are usable in treating and/or preventing a disease or condition which can be relieved by the retinoid X receptor ligand-dependent gene transcriptional regulation (for example, diseases caused by the expression of insulin resistance, hypertension, cerebrovascular diseases, rheumatoid arthritis, autoimmune disease, Ca metabolic disorder, complication of diabetes, arteriosclerosis, etc.). Moreover, they can inhibit denaturation and/or necrosis of pancreatic Langerhans islet &bgr;-cells and, therefore, are usable in making these cells to sustain the insulin productivity.