1. Fibre composition in the vastus lateralis muscle, and blood pressure, were determined in age-matched normotensive (n = 22) subjects and previously untreated patients (n = 19) with essential hypertension.
2. In all subjects the muscle fibres were classified, as fast-twitch (FT) and slow-twitch (ST), and blood pressure was recorded. Eleven patients and seven of the normotensive subjects participated in an extended haemodynamic study with intraarterial pressure measurements and determinations of leg blood flow.
3. In both normo- and hyper-tensive subjects, ambulant and intra-arterial blood pressure and leg vascular resistance were negatively correlated to the percentage of ST fibres; no significant correlation was found to total leg blood flow.
4. The findings show that muscles with a high proportion of FT fibres have a higher resistance than muscles rich in ST fibres and suggest that the type of fibre in skeletal muscle might be of importance for the development of the hypertensive disease.