A delivery agent for delivering a biologically active agent to a warm-blooded animal includes a hydrophobic moiety covalently bonded to a hydrophilic moiety. The hydrophobic moiety can include bile acids, sterols, or hydrophobic small molecules. The hydrophilic moiety can include α-amino acids, dipeptides or tripeptides, or hydrophilic small molecules. An illustrative delivery agent is Nα-deoxycholyl-L-lysine-methylester. The delivery agent and the biologically active agent are mixed together to form a complex, which is then administered to the animal. These complexes are particularly useful for oral administration of biologically active agents, but other routes of administration may be used.