A new, pharmacologically active morphine derivative, 6-succinylmorphine, was synthesized. The properties of this compound and evidence for its structure are presented. Succinylmorphine was covalently coupled to ethylamino-Sepharose. Morphine-Sepharose containing up to 40 mug of morphine did not block the electrically stimulated contraction of isolated guinea pig ileum, but after alkaline hydrolysis of beads containing 2 mug of morphine the supernatant completely blocked contraction. This block was reversed by the specific morphine antagonist naloxone. Antibodies to morphine were removed from serum by morphine-Sepharose, but not by ethylamino-Sepharose, providing evidence of the efficacy of the beads for affinity chromatography.