A four-generation transmission of 1qh+ chromosome was ascertained by routine chromosome analysis of a mildly dysmorphic and retarded 61/2-year-old female. Concordance between synophrys and the 1qh+ marker was the only consistent phenotypic relationship. The variant chromosome did not appear uncoiled, and Giemsa centromeric staining (C-bands) revealed an increased width of the heterochromatin commensurate with the increased length of the long arm. Giemsa banding of the entire chromosome (G-bands) revealed two heterochromatin bands, identical in appearance, in the centromeric region with the remainder of the chromosome showing normal banding. The distribution of Duffy blood groups in the pedigree was consistent with the locus being on chromosome No. 1.