Skinned fibres from striated muscle were used to study the intracellular mechanisms (contractile proteins and sarcoplasmic reticulum [SR]) of action of diltiazem (DT) and verapamil (VP) on muscle contraction. Rabbit papillary muscle (PM), and the skeletal muscles adductor magnus (AM, fast-twitch) and soleus (SL, slow-twitch) were used. The muscles were skinned by homogenization and fibre bundles for PM and single fibres for AM and SL were dissected from the homogenate and mounted on photodiode force transducers.