When olfactory receptor neurons respond to odors, a depolarizing Cl(-) efflux is a substantial part of the response. This requires that the resting neuron accumulate Cl(-) against an electrochemical gradient. In isolated olfactory receptor neurons, the Na(+)+K(+)+2Cl(-) cotransporter NKCC1 is essential for Cl(-) accumulation. However, in intact epithelium, a robust electrical olfactory response persists in mice lacking NKCC1. To determine whether NKCC1 is required for normal olfactory sensitivity, olfactory sensitivity was compared between knockout (KO) mice carrying a null mutation for NKCC1 and wild-type (WT) littermates. Using operant behavioral techniques, olfactory sensitivity was measured using a commercial liquid-dilution olfactometer. Detection thresholds for the simple odorants cineole, 1-heptanol, and 1-propanol were compared in KO and WT animals. Regardless of the stimulus conditions employed, no systematic differences in behavioral thresholds were evident between KO and WT animals. We conclude that NKCC1 is not required for normal olfactory sensitivity.