The metabolic fate of methyl n-butyl ketone (MnBK) and its isomer methyl isobutyl ketone (MiBK) was studied in mice. The concentrations of both ketones and their metabolites in blood and brain were measured at different time intervals after their administration. The principal metabolites of MnBK were 2-hexanol (2-HOL) and 2,5-hexanedione (2,5-HD), while those of MiBK were 4-methyl-2-pentanol (4-MPOL) and 4-hydroxy-4 methyl-2-pentanone (HMP). The administration of 2-hexanol by itself led to the appearance of both MnBK and 2,5-hexanedione which, when administered by itself, did not lead to the appearance of either MnBK or 2-hexanol. The administration of 4-methyl-2-pentanol resulted in the appearance of MiBK and HMP. The administration of HMP did not result in the appearance of MiBK or 4-MPOL. These results indicate that the metabolic fate of MnBK and MiBK is similar to that reported in other species.