Much personality research suggests that the variance in personality can be accounted for by a few dimensions, often hypothesized to be connected to neurological circuits. Gray's (1982) behavioural activation system (BAS) and behavioural inhibition system (BIS) in particular propose to explain for a variety of behaviour. This investigation sought to determine whether Positive Emotionality is an appropriate measure of the BAS, and how Tellegen's (1985) constructs are related to BAS activity. Measures of BAS and Positive Emotionality were administered to undergraduates. Confirmatory factor analyses revealed that, while Positive Emotionality can be used as an indicator of BAS activity, it is better conceived of as a distinct, correlated construct. In addition, not all components of Positive Emotionality were related to BAS activity, and BAS was further related to components of Negative Emotionality and Constraint. Copyright © 2004 John Wiley & Sons, Ltd.