The study examined the effects of reward and punishment on response disinhibition, happy and nervous moods, heart rate and skin conductance levels during performance of an instrumental learning task. For one group of subjects (the reward group), correct responses were reinforced with a small monetary reward, while for another group (the punishment group), incorrect responses led to a small loss of money. Results indicated that subjects in the punishment group made fewer disinhibitory responses, were more nervous and less happy, and had a higher skin conductance level compared with subjects in the reward group. For both groups, these measures (and heart rate) did not correlate with each other, or with trait impulsivity or trait anxiety. These findings are discussed in relation to Gray's theory of behavioural inhibition system (BIS) and behavioural approach system (BAS).