More than 50% of severe childhood deafness is genetically determined, approximately 70% of which occurs without other abnormalities and is thus termed nonsyndromic 1, 2. So far, 30 nonsyndromic recessive deafness loci have been mapped and the defective genes at 6 loci, DFNB1, DFNB2, DFNB3, DFNB4, DFNB9 and DNFB21, have been identified, encoding connexin-26 (ref. 3), myosin VIIA (ref. 4), myosin XV (ref. 5), pendrin 6, otoferlin 7 and α-tectorin 8, respectively. Here we map a new recessive nonsyndromic deafness locus, DFNB26, to a 1.5-cM interval of chromosome 4q31 in a consanguineous Pakistani family. A maximum lod score of 8.10 at θ= 0 was obtained with D4S1610 when only the 8 affected individuals in this family were included in the calculation. There are seven unaffected family members who are also homozygous for the DFNB26-linked haplotype and thus are non-penetrant. A dominant modifier, DFNM1, that suppresses deafness in the 7 nonpenetrant individuals was mapped to a 5.6-cM region on chromosome 1q24 with a lod score of 4.31 at θ= 0 for D1S2815.