A large number of mutations in rhodopsin are associated with autosomal dominant retinitis pigmentosa (A DRP). We analyzed the biochemical phenotypes of the ADRP-associated cysteine mutants C167R, C222R, and C264del. C222R behaved as wild type in every aspect testable and is classified as a class I mutant. C167R produced intact protein but did not regenerate with 11-cis retinal and was not transported to the plasma membrane. We confirm its classification as a class IIa mutant. C264del represents a novel phenotype, which we propose to call class III. It produced a truncated protein of 27 kDa that failed to regenerate with 11-cis retinal and was not targeted to the plasma membrane. (C) 2002 Elsevier Science (USA). All rights reserved.