3H-Dodecylcyclohexane was incorporated in rat diet in order to study the metabolic utilization by mammals of a monocycloparaffin chosen as a typical naphthenic constituent of mineral oils. Dodecylcyclohexane was largely absorbed. No elimination of the hydrocarbon was observed in urine while an extended excretion of 3H occurred via this route. About 7% of absorbed dodecylcyclohexane was stored in the carcass, while the rest was omega-oxidized to cyclohexyldodecanoic acid, which incorporated into neutral lipids and phospholipids. The aliphatic chain of this unusual fatty acid underwent the normal fatty acid degradation pathways, leading to even fatty acids, squalene, cholesterol and nonlipid resynthesis, while the cyclohexyl ring was eliminated as urinary metabolites. Incorporation of omega-cyclohexyl fatty acids in phospholipids may raise a point of toxicological significance which is to be investigated.