Objective:To explore the significance of genetic testing in the etiological diagnosis in deafness patients. Methods:A total of 200 unrelated individuals with nonsyndromic hearing loss of unknown etiology were recruited for the mutational screening,by using the methods of DNA microarray and direct sequencing. The mutations tested were 35delG,176del16bp,235delC and 299delAT in the GJB2 gene,C538T in the GJB3 gene,IVS7-2A>G and A2168G in the SLC26A4 gene,and A1555G and C1494T in the mitochondrial 12S rRNA gene. Results:Deafness-causing mutations were detected in 78 patients(39.0%),of which 59 subjects (29.5%) were diagnosed as hereditary hearing loss. The carrier frequencies of deafness-causing mutations in these patients were 18.5% in GJB2,14.0% in SLC26A4,1.0% in GJB3 and 5.5% in mitochondrial DNA 12S rRNA,respectively. Conclusion:Genetic factors account for almost 30% hearing-impaired subjects of unknown etiology. The results indicate the necessity of genetic screening for mutations of these causative genes in patients with nonsyndromic hearing loss.