A 32 kDa phospholipase A 2 inhibitory protein was isolated from pig thyroid gland after calcium precipitation and fast protein liquid anion-exchange chromatography. SDS-polyacrylamide gel electrophoresis revealed the purity of the protein. The protein activity was assessed by the inhibition of pancreatic phospholipase A 2 on [ 3H]oleic acid-labelled Escherichia coli membranes as substrate and on the prostaglandin E 2 production of cultured thyroid cells. The amino acid composition and the isoelectric point were quite similar to those of endonexin previously described in other tissues or cells. The cross-reactivity of a polyclonal antibody against a 32 kDa lipocortin from human peripheral blood mononuclear cells with our thyroidal 32 kDa protein confirmed its lipocortin nature. Before the purification by fast protein liquid chromatography, the Ca 2+ pellet contained lipocortin I (35 kDa and its core protein 33 kDa) identified by its cross-reactivity with a polyclonal antibody.