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The authors performed a differential conditioning experiment in 30 rats, using 2 odors as the conditioned stimuli (CS+ and CS−) and hypoxia (8%O2) as the unconditioned stimulus. Vanillin was the CS+ and rose the CS− in half of the rats, and vice versa in the other half. Fifteen paired CS+/hypoxia trials and 15 CS− only trials were performed in random order, followed by 3 CS+ only and 3 CS− only trials to test for conditioning. The increase in ventilation from prestimulus levels averaged 116 ± 85% in response to CS+ versus 55 ± 36% in response to CS−. This effect was supported by the significant Pre–Post Stimulus × CS Type interaction for this variable (p < .003). The data confirm the sensitivity of breathing to conditioning processes and also indirectly support the hypothesis that feedforward responses may complement feedback reflex pathways in respiratory homeostasis.