Extracts of porcine anterior pituitary contain several corticotrophic variants of ACTH 1-39. They were isolated by adsorption chromatography, ion-exchange chromatography and reverse-phase high-performance liquid chromatography. Four variants were then identified as starting and ending at positions corresponding to ACTH 1-38, 1-37, 7-39 and 7-38. Several of these fragments were recovered in chromatographically multiple forms. Although all fragments isolated had corticotrophic activity (measured on isolated rat adrenal cells) those with a shortened N-terminal region had a lower potency than those with an intact N-terminal region. Corticotrophic activity of porcine ACTH 7-38 was detected in a preparation with a beta-aspartyl shift at position 25. However, in agreement with previous studies, synthetic human ACTH 7-38, in which an intact Asn-Gly bond was structurally proven, possessed no such activity. The results indicate that position 25 as well as positions 1-6 are important for corticotrophic activity, and that a deamidative beta-aspartyl shift at position 25 can influence the activity.