The deletion of guanine at position 35 (35delG) of connnexin 26 (GJB2) gene is a frequent cause of genetically determined deafness in many Caucasian populations. To study the frequency of carriage of 35delG mutation in the population of central Poland we analysed a group of 888 unrelated persons (adults and newborns, selected randomly regardless of the hearing status). The frequency of carriers of the 35delG mutation was found to be 4.1% and the gene frequency of the mutated allele was 2.1%. These data suggest that, in Poland, 35delG mutation in GJB2 has relatively high frequency and is a significant etiological factor causing hearing loss (it may be responsible for 20%-40% of all cases of congenital deafness and as much as 33%-66% of all cases of genetically determined deafness). [ABSTRACT FROM AUTHOR]