The thesis revisits antitrust law’s intra-enterprise conspiracy doctrine in the context of affiliated corporations. After an analysis of the doctrine, its tension with the inevitable cooperation in a corporate group, and the reasons for its rejection in a limited setting by the Supreme Court, the paper goes on to explore the groundings for a broader solution. It clarifies how far the lower courts have extended the Supreme Court’s rationale and suggests a consistent standard as to when corporate groups form a single economic unit for purposes of section 1 of the Sherman Act. According to this standard, courts should assess on a case-by-case basis whether a parent corporation can control its subsidiary. There should be a rebuttable presumption for the existence of such potential control when the parent owns a majority of the subsidiary’s voting and common stock. To the contrary, when a parent owns less than a majority the rebuttable presumption should be that the corporations have conspiratorial capacity for antitrust purposes.