Drug delivery conjugates of including a BAL C-tail peptide including all or a portion of the carboxy terminal region of human bile salt-activated lipase (BAL) conjugated to a biologically active substance are described. The C-tail peptide-drug conjugates, when orally ingested, compete with native BAL in binding to the intestinal surface, and, as a result, permit drug compositions to be delivered specifically to the intestine. Useful C-tail peptides are derivatives of the carboxy terminal region of BAL derived from all or portion of the region containing amino acid residues 539 to 722, and have a mucin-like structure containing at least three of the repeating proline-rich units of eleven amino acid residues each.