The modified Golgi staining method was used to study the sarcoplasmic reticulum (SR) and t- tubules of skeletal muscle in central core disease. Significant pathological changes were documented in both of these organelles in seven patients. Pathological changes were seen in both core and non-core regions, with the abnormalities being greatest in the cores. In noncore regions, distortions in the normal anatomy were minor. In cores, there was much more significant distortion of the normal anatomy and also an increase in the amount of SR and number of t-tubules.