Choice behaviour and extinction learning were studied in a group of 108 undergraduates classi®ed according to the Sensitivity to Punishment and Sensitivity to Reward scales (that measure Gray's anxiety and impulsivity dimensions, respectively). The learning task consisted of continuous choosing between two response alternatives: one was continuously reinforced with a small reward and the other was partially reinforced with a greater reward. After 200 trials, one of the responses remained as in the previous phase, and the other was never rewarded in order to attain extinction. The main aims of the study were: (i) to replicate Avila's ®nding of lesser resistance to extinction of subjects having high scores on the Sensitivity to Punishment scale; (ii) to investigate whether impulsives (subjects having high scores on the Sensitivity to Reward scale) chose more than non-impulsives the response associated with a continuous, small reward; and (iii) to test, following the model of Patterson and Newman, whether impulsive subjects had a great resistance to extinction of responses highly associated with reward. Results supported all three predictions. Discussion is based on the compatibility of the models of disinhibition of Gray and of Patterson and Newman.