Rats were given standard avoidance training in a two-compartment shuttle-box. Thereafter shock was only signalled if the subject was in one of the distinctively coloured compartments at the start of a given trial, while non-signalled shock was presented in the other compartment. Subjects showed a significant preference for this compartment on several measures. Half of the subjects received a relatively higher shock intensity during this latter part of the experiment, and this had the effect of improving avoidance performance and increasing the subjects' preference for the signalled shock situation. These findings are discussed in terms of the relative conditioned aversiveness of various stimuli present in the situation.