The Usher syndromes (USH) are autosomal recessive diseases characterized by congenital sensorineural hearing loss and progressive pigmentary retinopathy. While relatively rare in the general population, collectively they account for approximately 6% of the congenitally deaf population. Usher syndrome type II (USH2) has been mapped to chromosome 1q (W. J. Kimberling, M. D. Weston, C. Möller, et al., 1990, Genomics 7: 245-249; R. A. Lewis, B. Otterud, D. Stauffer, et al., 1990, Genomics 7: 250-256), and one form of Usher syndrome type I (USH1) has been mapped to chromosome 14q (J. Kaplan, S. Gerber, D. Bonneau, J. Rozet, M. Briord, J. Dufier, A. Munnich, and J. Frezal, 1990. Cytogenet. Cell Genet. 58: 1988). These loci have been excluded as regions of USH genes in our data set, which is composed of 8 French-Acadian USH1 families and 11 British USH1 families. Both of these sets of families show linkage to loci on chromosome 11. Linkage analysis demonstrates locus heterogeneity between these sets of families, with the French-Acadian families showing linkage to D11S419 (Z = 4.20, theta = 0) and the British families showing linkage to D11S527 (Z = 6.03, theta = 0). Genetic heterogeneity of the data set was confirmed using HOMOG and the M test (log likelihood ratio > 10(5)). These results confirm the presence of two distinct USH1 loci on chromosome 11.