The role of the conditioned stimulus (CS) as a determinant of the form of the Pavlovian conditioned response (CR) was investigated in five experiments. Both stabilimeter measures of general activity and detailed observations of the behavior of the rat subjects in the presence of CSs anticipatory to a food unconditioned stimulus (US) were obtained. In Experiment 1, substantially different behaviors to light and tone CSs were observed; further, these differences were found to be dependent on specific learning experience rather than on the mere presence of different stimulation at the time of response evocation. Experiments 2 and 3 investigated the possibility that there was considerable communality of learning to light and tone CSs despite their evoking different CRs. In Experiment 2, prior conditioning of either the tone or light CS was found to block the acquisition of various behaviors to the added element when a light-tone compound stimulus was reinforced, even though the pretrained stimulus did not itself evoke those behaviors. In Experiment 3, the nature of second-order conditioned responding was found to be similar regardless of which first-order CS was used as the reinforcer. Additionally, the reinforcing powers of the light and tone CSs were found to summate. Experiments 4 and 5 examined behaviors to a variety of visual and auditory stimuli paired with food. Stimulus modality and the localizability and vertical location of visual stimuli were found to influence conditioned responding. These results suggested that in this conditioning situation, similar learning of a CS-US relation may be displayed in different overt CRs, depending on the nature of the CS.