To identify the relationship between mutation in the insulin receptor substrate-1 (IRS-1) gene and the incidence of non-insulin-dependent diabetes mellitus (NIDDM) in the Chinese population.Samples were obtained from 68 Chinese patients with NIDDM and 68 control subjects. The +1700-(+)4437 bp fragment of the IRS-1 gene was screened by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. All SSCP variations were submitted to DNA sequence analysis.Two amino acid variations [GGG-->AGG (G971 R) and CCT-->TCT (P1079 S)] and 3 silent mutations [GAT-->GAC(D422D), CCA-->CCC(P737 P) and GCA-->GCG (A804 A)] were identified, among which the CCA-->CCC(P737 P) and CCT-->TCT(P1079S) have not been previously reported. All five variations were found in Chinese patients with NIDDM, while GCA-->GCG(A804A) was the only one found in control subjects. The overall incidence of the five variations in Chinese patients with NIDDM were much higher than that in control subjects (38.2% vs 7.4%, chi 2 = 18.42, P GCG (A804A), and its frequency was significantly higher in Chinese patients with NIDDM than in controls (26.5% vs 7.4%, chi 2 = 8.84, P 0.05).These results indicate that there may be a relation between these nucleotide variations of IRS-1 gene and Chinese patients with NIDDM.