This research describes an analysis, using event-study methodology, of the reaction of the stock returns of a sample, drawn from the one-hundred largest bank holding companies, to certain actions of regulatory agencies. The first part of the analysis examines the reaction of the bank stocks to the closure of the Bank of New England, using cross-sectional variables not previously examined by other investigators. The second event considers the invalidation of interest-rate swap contracts by the British Law Lords, the highest court in Britain. The third case is an examination of the effects of actions taken to enforce the Community Reinvestment Act. All three events have significant abnormal returns in at least one sub-sample and event window. The results of the cross-sectional analysis and the lack of response to later events are consistent with market efficiency in the semi-strong form. The results are also consistent with the hypothesis that regulatory policies that emphasize consistency and banking system safety are desirable.