OBJECTIVES: The principal objective of the present paper was to investigate the utility of an extended theory of planned behaviour (TPB) for discriminating between stages of the transtheoretical model (TTM). DESIGN: Congruent with Sutton (2000) a cross-sectional design was employed. The study (N = 331) investigated the TPB and TTM in the domain of health-related food choice. METHOD: The study utilized a questionnaire methodology. The data were analysed using analyses of variance and polynomial contrast analyses. RESULTS: Results showed a significant linear trend for all TPB variables across TTM stages, although there were significant quadratic relationships between TTM stage and both subjective norm and behavioural intention. Hierarchical regression analyses indicated that TTM stage might best be regarded as a proxy measure of behaviour. CONCLUSIONS: The present study provides evidence to support the utility of the TPB but casts doubt on the TTM. Further research is required to evaluate the effectiveness of interventions targeted at individuals in certain stages with variables informed by the TPB, and to extend the present findings beyond the domain of health-related food choice.