This study compared a motivational intervention based on protection motivation theory (PMT, Rogers, 1975, 1983) with the same motivational intervention augmented by a volitional intervention based on implementation intentions (Gollwitzer, 1993).The study had a longitudinal design, involving three waves of data collection over a 2-week period, incorporating an experimental manipulation of PMT variables at Time 1 and a volitional, implementation intention intervention at Time 2.Participants (N=248) were randomly allocated to a control group or one of two intervention groups. Cognitions and exercise behaviour were measured at three time-points over a 2-week period.The motivational intervention significantly increased threat and coping appraisal and intentions to engage in exercise but did not bring about a significant increase in subsequent exercise behaviour. In contrast, the combined protection motivation theory/implementation intention intervention had a dramatic effect on subsequent exercise behaviour. This volitional intervention did not influence behavioural intention or any other motivational variables.It is concluded that supplementing PMT with implementation intentions strengthens the ability of the model to explain behaviour. This has implications for health education programmes, which should aim to increase both participants' motivation and their volition.