Fourteen workers renovating an old house in Québec developed histoplasmosis, a respiratory disease caused by inhaling fungus spores. Bats and birds can excrete the organism in their droppings and it can persist in the environment for several years. Outbreaks can occur when demolition work produces dust containing such droppings. Approximately 30 workers and residents were exposed to dust from bird or bat droppings previously hidden in the brick walls. Two of the affected workers were hospitalized.