The capacity for sparteine (SP) metabolism was determined in 48 Caucasian subjects by measuring amounts of drug and dehydrogenated metabolites in urine after an oral dose of SP sulfate. Three phenotypes were recognized and were assumed to represent individuals homozygous for poor SP oxidation (group III) and those heterozygous (group II) and homozygous (group I) for extensive SP oxidation. Separation of groups I and II, although incomplete, was improved by alterations in the published analytic procedure. The pattern of deviations from the normal distribution was similar for both dehydrosparteine metabolites. This supports the hypothesis of a common intermediate, the formation of which is monogenically controlled. Correlation analysis of the two metabolites indicates the possibility of further metabolism of 5‐dehydrosparteine.Clinical Pharmacology and Therapeutics(1982)31, 23–29; doi:10.1038/clpt.19