The PCR/restriction endonuclease digestion (RE) assay and PCR/SSCP analysis of the rhodopsin gene in 13 Japanese families with autosomal dominant retinitis pigmentosa (ad RP) revealed a G-A substitution of the first nucleotide of codon 181, replacing Glu (GAG) with Lys (AAG), in one family. The proband showed an early onset of symptoms in childhood with a diffuse loss of rod and cone function and a relatively good preservation of cone function, corresponding to the type with relatively rapid progression to blindness (type I category of ad RP).