The present invention comprises a method for delivering pharmaceutical and/or imaging agents within and/or through the dermal, mucosal and other cellular membranes, and across the blood-brain barrier, utilizing a fusogenic protein. The fusogenic protein is associated with a phospholipid membrane, such as a liposome. The liposome may include dioleoylphosphatidylserine, a negatively charged long-chain lipid. Alternatively, the liposome is comprised of a mixture of negatively charged long-chain lipids, neutral long-chain lipids, and neutral short-chain lipids. Preferred fusogenic proteins include saposin C and other proteins, polypeptides and peptide analogs derived from saposin C. The active agent contained within the liposome may comprise biomolecules and/or organic molecules. This technology can be used for both cosmetic and medicinal applications in which the objective is delivery of the active agent within and/or beneath biological membranes or across the blood-brain barrier and neuronal membranes.