As part of the search for the Huntington disease (HD) gene we have cloned and sequenced 34 kb of genomic DNA containing the full-length gene for the β-subunit of the human cGMP phosphodiesterase (β-cGMP PDE). This gene is localized to 4p16.3 about 700 kb proximal to the 4p telomere and represents the most telomeric gene characterized on 4p to date. We show that this gene is comprised of 22 exons spanning approximately 43 kb of genomic DNA. We also provide 400 bp immediately 5′ to the putative initiator methionine and 700 bp of 3′ flanking sequences. Northern blot analysis of several human tissues revealed a highly abundant 3.5 kb transcript and a minor signal of 4.5 kb in retinal tissue. Alignment of the deduced amino acid sequence to the previously identified β-subunits of the cGMP PDEs of mouse and cow demonstrates highly significant similarities and, therefore, confirms the identity of the cloned gene. A defect in the β-subunit of the cGMP PDE gene has been shown recently to be the cause for the retinal degeneration in the rd mouse. The cloning of the human homolog and the knowledge of its genomic organization with exon/intron boundaries will allow rapid assessment of the role of this gene in the causation of human retinopathies.