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We report the results of a comparative study of the molecular order and dynamics of phosphatidylcholine (PC) bilayer membranes in the absence and presence of cholesterol, ergosterol and lanosterol, using deuterium (²H) nuclear magnetic resonance (NMR) of deuterated phospholipid molecules, in addition to solid state ¹³C and ³¹P-NMR. Using dimyristoylphosphatidylcholines (DMPCs) specifically labeled at positions 2′, 3′, 4′, 6′, 8′, 10′ and 12′ of the sn-2 chain together with the perdeuterated 2-[²H₂₇]DMPC derivative, the order profile for 9 of the 13 methylene groups of the sn-2 chain was established at 25°C for DMPC, DMPC/cholesterol, DMPC/ergosterol and DMPC/lanosterol membranes, at a fixed sterol/phospholipid mol ratio of 30%, and in the presence of excess water. The overall ordering effects were found to be ergosterol > cholesterol ⪢ lanosterol. Transverse relaxation (T_2e) studies of …