The ability of a series of molecular umbrellas, derived from cholic acid, L-lysine, spermidine, and Cascade Blue, to cross fluid liposomal membranes made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine(POPC)/1-patmitoyl-2-ole oyl-sn-glycero-3-phosphatidylglycerol (POPG) (95/5, mol/mol) has been determined. In sharp contrast to the classic "size/lipophilicity" rule of membrane transport, those molecular umbrellas that were larger in size and less lipophilic crossed these liposomal membranes more readily. The likely origin for this unusual behavior is briefly discussed.