There is considerable variety among the clinical features of autosomal dominant retinitis pigmentosa (ADRP). This is probably at least in part due to genetic heterogeneity. Recently, various mutations of the rhodopsin gene have been detected in some ADRP families. We report on six patients from two families with ADRP who were investigated by means of psychophysical and electrophysiological methods. All displayed the same rhodopsin gene mutation at codon 347, which exchanges the amino acid proline for leucine (pro-347-leu). The patients had early-onset night blindness and impaired side vision as of the end of their second life decade. They produced monophasic dark-adaptation curves, showing a lack of rod function and elevated cone thresholds. Dark-adapted two-color threshold perimetry using 500- and 650-nm stimuli revealed a diffuse loss of rod function and centrally preserved cone function. The electroretinogram was nonrecordable at the age of about 30 years. A certain variability of visual function loss was noted among patients in the overall severe course of the disease, but the clinical findings of this genotype corresponded to type 1 ADRP of Massof and Finkelstein in all cases.