Pallid is one of 12 independent murine mutations with a prolonged bleeding time that are models for human platelet storage pool deficiencies in which several intracellular organelles are abnormal. We have mapped the murine gene for protein 4.2 (Epb4.2) to chromosome 2 where it co-localizes with pallid. Southern blot analyses suggest that pallid is a mutation in the Epb4.2 gene. Northern blot analyses demonstrate a smaller than normal Epb4.2 transcript in affected pallid tissues, such as kidney and skin. This is the first gene defect to be associated with a platelet storage pool deficiency, and may allow the identification of a novel structure or biological pathway that influences granulogenesis.