1. The disposition of ¹⁴C-methyl ethyl ketoxime (MEKO) was determined in the male F344 rat following oral, intravenous (i.v.) and dermal administration. 2. Oral doses of 2.7, 27 and 270 mg/kg were primarily excreted as CO₂ (71-49%) in decreasing percentage as the dose increased. Excretion in urine (13-26%) and as volatiles (5-18%) increased as the dose increased. Five to 6% of the dose remained in the major tissues after 72 h. 3. An i.v. dose of 2.7 mg/kg was also principally excreted as CO₂ (48.8%) with excretion in urine and as expired volatiles accounting for 21.4 and 11.4%, respectively. About 7% of the administered radioactivity remained in the tissues after 72 h. 4. Following dermal administration, 13 and 26% of a 2.7 and 270 mg/kg dose, respectively, were absorbed. Volatilization from the dose site prior to placement in the metabolism cage may account for the low absorption. 5. MEKO was biotransformed to at least five polar metabolites that could only be partially resolved by anion exchange chromatography. Incubation with glucuronidase, but not sulphatase, changed the urinary metabolic profile. Methyl ethyl ketone was a major component in the volatiles.