All rights reserved. Studies of lateral heterogeneity in cell membranes are important since they help to understand the physical origin of lipid domains and rafts. The simplest membrane mimics are hydrated bilayers composed of saturated and unsaturated lipids. While their atomic structural details resist easy experimental characterization, important insight can be gained via computer modeling. We present the results of all-atom molecular dynamics simulations for a series of fluid one-and two-component hydrated lipid bilayers composed of phosphatidylcholines with saturated (dipalmi-toylphosphatidylcholine, DPPC) and mono-unsaturated (dioleoylphos-phatidylcholine, DOPC) acyl chains slightly differing in length (16 and 18 carbon atoms, respectively). As a results, it was shown that the bilayers' properties are tuned in a wide range by the chemical nature and relative content of lipids. The impact that the micro-heterogeneity may have on formation of lateral domains in response to external signals is discussed. Understanding of such effects creates a basis for rational design of artificial membranes with predefined properties.