Background: Insulin detemir and insulin glargine are synthetic long-acting insulin analogs. In people, insulin glargine is longer acting and has a relatively flat time-action profile, while insulin detemir has significantly less within-subject variability. Insulin detemir is also associated with less undesired weight gain and decreased frequency of hypoglycemic events.Objectives: To compare the pharmacodynamics of insulin detemir and insulin glargine in healthy cats. Animals: Ten young, healthy, neutered, purpose-bred cats. Methods: Randomized, cross-over design. Pharmacodynamics of insulin detemir and insulin glargine were determined by the isoglycemic clamp method after a 0.5 U/kg SC injection.Results: The only significant difference in the pharmacodynamics of insulin detemir and insulin glargine was onset of action (1.8 AE 0.8 and 1.3 AE 0.5 hours for insulin detemir and insulin glargine, respectively, P 5 .03). End of action of insulin detemir was reached at 13.5 AE 3.5 hours and for insulin glargine at 11.3 AE 4.5 hours (P 5 .18). Time-to-peak action of insulin detemir was reached at 6.9 AE 3.1 hours and for insulin glargine at 5.3 AE 3.8 hours (P 5 .7). The time-action curves of both insulin analogs varied between relatively flat curves in some cats and peaked curves in others.Conclusion and Clinical Importance: Insulin detemir and insulin glargine have shorter durations of action than in people when assessed by the clamp method, but in some cats these insulin analogs could be useful as once-a-day drugs. Peak effects of both insulin analogs are pronounced in some cats.