Mutations in the Cx26 (GJB2) gene have been shown to be responsible for a major part of autosomal recessive non-syndromic inherited prelingual deafness. We have sequenced the coding region of GJB2 gene from 169 Taiwanese patients with prelingual deafness and 100 unrelated normal individuals. In the deaf patients, three mutations were found: two novel mutations, 551G-->A, and 299-300delAT, and one previously described mutation, 235delC. Four previously reported polymorphisms, 79G-->A, 109G-->A, 341A-->G, and 608T-->C, were also found in both deaf patients and normal individuals and one new possible polymorphism, 558G-->A, which was only found in a patient. Interestingly, we did not find the 35delG allele, which is commonly found in the Caucasian population, either in the patients or in normal individuals we examined. Our data also showed 235delC to be the most common type of mutation found in Cx26 mutants (approximately 57%). Therefore, based on our findings, we have developed a simple molecular test for the 235delC mutation and it should be of considerable help to those families to understand the cause of their children having the prelingual deafness.