Four experiments using barpress conditioned suppression in rats found that tone evoked more freezing (immobility) than did light. Still, tone and light appeared to have similar conditioned value as assessed by suppression in Experiments 1, 2, and 3, and by blocking, second-order conditioning, and overconditioning assays in Experiments 1, 2, and 3, respectively. Experiment 4 arranged for tone to evoke less suppression than light but more freezing. Results suggest that in fear conditioning, the nature of the conditioned stimulus affects the form of conditioned responding (strong vs. weak freezing). This conclusion extends one drawn by P. C. Holland (1977) on the basis of his work in appetitive conditioning.The most thorough demonstration that the nature of the conditioned stimulus (CS) affects the form of the conditioned response (CR) is that of Holland (1977). Using rats in an appetitive situation, Holland found that tones paired with food evoked head-jerk and startle CRs, whereas lights paired with food evoked the CRs of rearing and orienting toward the food tray. Holland then asked whether these different behaviors might reflect different conditioned values of tone and light. In separate experiments, he assessed those values in two ways: (a) by measuring the ability of tone and light to serve as blockers in Kamin's (1968) two-stage blocking procedure and (b) by assessing their ability to serve as second-order reinforcers. In the blocking experiment, Holland paired a tone + light compound CS with food. He found that if the light had previously been conditioned, it would block the conditioning of head-jerk and startle to the formerly neutral tone. If the tone had previously been conditioned, it would block the conditioning of tray orientation to the formerly neutral light. It is notable that in each case, the blocker had the ability to block the conditioning of a behavior that it rarely evoked itself. In