The study was based on plasma samples taken on enrollment from a subset of the 6,105 subjects in the Perindopril Protection Against Recurrent Stroke Study (PROGRESS). The PROGRESS was an international, randomized, double-blind controlled study of a perindopril-based blood pressure lowering regimen among individuals with stroke or transient ischemic attack within the previous five years. Coordination and monitoring for PROGRESS were maintained through two international coordinating centers, one in Sydney, Australia and the other in Auckland and through seven regional coordinating centers in Beijing, Glasgow, Melbourne, Milan, Osaka, Paris and Uppsala. There were 172 local clinical centers distributed through 10 countries: Australia, Belgium, China, France, Ireland, Italy, Japan, New Zealand, Sweden and the United Kingdom.