Secondary hyperparathyroidism has a significant impact on morbidity and mortality in advanced chronic kidney disease (CKD).Both nonselective and selective vitamin D receptor activators (VDRAs) are demonstrated in many studies for their efficacy on suppression of PTH. Most of them are quite expensive and unavailable in many countries. Calcitriol and alfacalcidol are less expensive and worldwidely distributed. There is only one short-term study which directly compares these two drugs. This study demonstrates that calcitriol is superior to alfacalcidol. However, alfacalcidol is a prohormone of calcitriol. It has to be converted by 25-hydroxylase at the liver to generate 1,25-dihydroxyvitamin D3 to act on target cells. Many pharmacokinetics studies demonstrate that alfacalcidol has lower AUC compared to calcitriol if they are administered in the same dose. Therefore, the authors hypothesize that alfacalcidol may be equivalently efficacious as calcitriol if its dose is adjusted according to the pharmacokinetics studies.