Transport molecules include a dendrimer and a biologically active molecule. The dendrimer of such transport molecules includes at least one guanidine group, at least one protonated guanidine group, at least one protected guanidine group, at least one amidine group, at least one protonated amidine group, at least one protected amidine group, at least one ureido group, at least one protonated ureido group, at least one protected ureido group, at least one thioureido group, at least one protonated thioureido group, or at least one protected thioureido group. The biologically active molecule is bonded to the dendrimer. A method of increasing the bioavailability of a drug includes bonding the drug to a dendrimer of the invention.