The effects of selective beta 2-adrenergic blockade with ICI 118,551 on the histochemical, biochemical, and contractile properties of slow-twitch soleus muscle from spontaneously hypertensive (SHR) and normotensive (WKY) rats were examined from birth to 8-10 weeks of age. Chronic treatment of normotensive rats with ICI 118,551 caused an impairment in the differentiation of slow type fibers during development but failed to alter the fiber type distribution of hypertensive rats. beta 2-Adrenoreceptor blockade was ineffective in reducing the enhanced glycolytic and oxidative capacities of soleus in hypertensive rats. The suggestion can be made that beta 2-adrenoreceptor activation is not responsible, at least directly, for the histochemical and biochemical alterations of slow muscle from hypertensive rats.