The s15DttMb, s36Pub, s1Acrg and s24Pub piebald deletion alleles belong to a set of overlapping deficiencies on the distal portion of chromosome 14. Molecular analysis was used to define the extent of the deletions. Mice homozygous for the smallest deletion, s15DttMb, die shortly after delivery and display alterations in the central nervous system, including hydrocephalus and a dorsally restricted malformation of the spinal cord. These mice also display homeotic transformations of vertebrae in the midthoracic and lumbar regions. Homozygous s27Pub mice contain a point mutation in the piebald gene, survive to weaning, and display no central nervous system or skeletal defects, arguing that the s15DttMb phenotype results from the loss of genes in addition to piebald. A larger deletion, s36Pub, exhibits additional cartilage malformations and defects in the anterior axial and cranial skeleton. The skeletal defects in both s15DttMb and s36Pub mice resemble transformations associated with the targeted disruption of Hox genes and genes encoding the retinoic acid receptors, which play a role in the specification of segmental identity along the anteroposterior axis. Complementation analysis of the s15DttMb and s36Pub phenotypes, using two additional deletions, localized the gene(s) associated with each phenotype to a defined chromosomal region.