This article explores questions of proof and precaution in the context of Canada's new Chemicals Management Plan. That plan includes a bold initiative known as the ‘Challenge’, under which the government has identified 200 high priority chemicals for which it is ‘predisposed’ to a finding of toxicity. The presumption will operate unless the challenged stakeholders submit ‘information’ sufficient to rebut it. Through comparison with the European REACH regulation, this article explores exactly what burdens have been shifted, to whom and why. It also evaluates the significance of this move for the governance of chemicals in Canada and for the health of Canadians. It looks specifically at the case of Bisphenol A, which was one of the 200 chemicals included in the Challenge, and was recently declared toxic under that process. The Challenge forces us to confront the ‘dilemma of industry data’, which complicates the debate over a shifted burden of proof in the context of chemicals management.