1. The object of this study was to determine whether meat protein per se is responsible for the higher blood pressures (BP) in omnivores compared with vegetarians. 2. Assessments were made by a double blind randomized control trial in 64 normotensive volunteers recruited from Royal Perth Hospital staff. 3. All volunteers were given a 'meat' substitute during the 2 week control period. Randomization was then introduced into two dietary groups: the first remained on the 'meat' substitute, and the other received a 'non-meat' substitute of vegetable protein, for the remaining 12 weeks of the trial. 4. The content of 'meat' and 'non-meat' substitute was designed quantitatively and qualitatively to represent the protein intake in recently studied diets of Australian omnivores and ovo-lacto vegetarians, respectively. The levels of fats (saturated and unsaturated), fibre, energy, Na+, K+, Mg2+, Ca2+ and carbohydrate in the intervention diets were similar. 5. These dietary changes were not associated with any significant changes in BP. Significantly lower urinary 3-methyl histidine excretions in volunteers receiving 'non-meat' supplements compared with the 'meat' eaters confirmed the dietary changes. 6. It was concluded that BP differences between omnivores and accultured vegetarians are unlikely to be due to differences in protein intake.