Given that there are a number of incentives for antitrust plaintiffs to sue in English courts, English jurisdictional decisions in such actions are of far-reaching importance for the future of private antitrust enforcement in the European Community. In Provimi, the High Court of England and Wales recently handed down one of the first judgments in Europe regarding the vitamins cartels and asserted its jurisdiction. The question before the High Court was whether vitamins purchasers have an arguable claim against a subsidiary of a cartelised manufacturer, where the subsidiary implemented the cartel without knowledge of the price-fixing agreement, and whether such a claim could arise even if there was no contractual relationship between the purchasers and the subsidiary in question. The High Court held that there was an arguable claim and that it had jurisdiction to hear claims against non-English subsidiaries as long as one of the subsidiaries was domiciled in the United Kingdom. This case note argues that the High Court was right to assume that there was an arguable claim, but that its reasoning is deficient. Invoking the European law principle of effectiveness, it argues in favour of easing or reversing the burden of proof for particular facts in private antitrust litigation. This case note also takes issue with the interpretation of certain jurisdictional agreements in the decision, which – if construed correctly – would have barred the High Court from finding that it had jurisdiction in respect of some of the claims.