THE gene for autosomal dominant retinitis pigmentosa in a large pedigree of Irish origin has recently been found to be linked to an anonymous polymorphic sequence, D3S47 (C17), from the long arm of chromosome 3 (refs 1, 2). As the gene coding for rhodopsin is also assigned to the long arm of chromosome 3 (refs 3, 4) and is expressed in rod photoreceptors that are affected early in this blinding disease⁵, we searched for a mutation of the rhodopsin gene in patients with autosomal dominant retinitis pigmentosa. We found a C→A transversion in codon 23 (corresponding to a proline →histidine substitution) in 17 of 148 unrelated patients and not in any of 102 unaffected individuals. This result, coupled with the fact that the proline normally present at position 23 is highly conserved among the opsins and related G-protein receptors⁶, indicates that this mutation could be the cause of one form of autosomal dominant retinitis pigmentosa.