In two experiments, rats were trained on a successive go/no-go discrimination problem in the runway in which the positive (8+) and negative (8-) discriminanda were differentiated by the presence or absence of a distinctive feature. The feature in Experiment 1 was a series of flash ing lights over the runway. In Experiment 2, the feature was a pretrial reinforcement (Phase 1), or pretrial reinforcement versus pretrial nonreinforcement (Phase 2). The feature signaled S+ trials in feature-positive (FP) groups and S- trials in feature-negative (FN) groups. The original discrimination was reversed in Phase 2 of both experiments. With the exception of the pretrial nonreinforcement groups in Experiment 2, there was an asymmetry in discrimination learning in both phases of both experiments favoring superior discrimination learning by FN subjects over FP subjects, a feature-negative effect. Implications of the results for an informa tion processing account of asymmetries in learning feature discriminations are discussed. Jenkins and Sainsbury (1969) reported an asym metry in pigeons' learning of a successive go/no-go discrimination in which the positive (S+) and neg ative (S-) discriminanda were differentiated by a distinctive stimulus (feature), presented on S+ trials in the feature-positive (FP) case and on S- trials in the feature-negative (FN) case, in the direction of faster learning of FP discriminations than FN dis criminations. This asymmetry, called the feature positive effect (FPE), is quite pervasive, having been obtained across a considerable range of experimental procedures, learning tasks, types of features, and species (see Hearst, 1978, in press, for reviews). The generality of the FPE has been taken to indicate that a fundamental psychological principle (or bias), per haps due to the innate organization of the nervous system, underlies its occurrence (Hearst, 1978; Newman, Wolff, & Hearst, 1980). Hearst (in press) has suggested that the FPE may be related to some effects in human learning and information process ing characterized by a bias favoring the presence over the absence of a stimulus as a source of information. The two experiments reported here investigated feature-discrimination learning in rats, employing for the first time a successive go/no-go discrimina tion problem in the runway. Previous feature-learning experiments with rats have demonstrated a FPE in appetitive barpress situations (Crowell & Bernhardt, 1979; Halgren, 1974, Lea, 1974) and in conditioned suppression (Reberg & Leclerc, 1977). Whether the