This paper establishes that the relative proportion of amobarbital metabolites in urine is highly variable from person to person and that observations of plasma half‐life give no indication of this variability, but it shows that a valid estimate of a given person's metabolite pattern can be obtained by studying a single urine specimen in the postdistributive phase. The two metabolites which were measured in urine accounted on the average of 9 subjects for 80% ± 3% of the dose with a range from 66% to 94%. The two metabolites were the well known 3′‐hydroxyamobarbital (COH) as a product of side chain hydroxylation and N‐β‐D‐glucopyranosyl amobarbital (N‐glu), a glucose conjugate which at some earlier time had been mistaken for an N‐hydroxylation product. Among 129 volunteer subjects, the metabolite ratio N‐glu/COH showed a median value of about 0.5 with a range from 0 to 2.8. A virtual absence of N‐glu was observed in one of the 129 subjects and confirmed by a second administration of amobarbital 3 mo later. Of the 14 subjects with predominant N‐glu excretion 4 were of Chinese origin, while there were 6 Chinese among the 115 other subjects (p < 0.02).