1. Weanling rabbits were made rachitic either by a vitamin D-deficient diet or by parenteral administration of ethane 1-hydroxy-1,1-diphosphonate (EHDP) in amounts sufficient in other species to block the formation of 1,25-dihydroxycholecalciferol [1,25-(OH)2D,].
2. The uptake of calcium into the isolated sarcoplasmic reticulum from mixed striated quadriceps muscle, and the amount of troponin C (the calcium-binding component of the troponin complex) in relation to other proteins from the same muscle, were measured.
3. In muscle from animals made rachitic by a dietary deficiency of vitamin D, the rate of uptake of calcium by the sarcoplasmic reticulum and the troponin C concentration were both significantly less (P < 0·02) than in control littermates. In EHDP-treated animals no significant differences from controls were found.
4. These results show that dietary deficiency of vitamin D in such animals can affect muscle physiology. Since no changes are found in animals made rachitic with EHDP, who presumably have a selective deficiency of 1,25-(OH)2D3, it is possible that the effect of vitamin D on muscle is mediated through metabolites other than 1,25-(OH)2D3 such as 25-hydroxycholecalciferol.