The aim of the GDMSP was to monitor the grain worker’s respiratory health and examine its association with dust levels in the work environment. It was run by Labour Canada in parallel with the Environmental Surveillance Program. All employees in five regions of Canada who had been continuously employed in the grain industry for longer than 90 days during a period of one year or intermittently for a total of six months in three years were invited to be a part of the study. Participants were assessed every three years across five waves from 1978 to 1993 in an open cohort. Over 14,000 participants completed a baseline assessment across each of these five waves.