The subjects were male swine producers, between 16 and 60 years of age, identified from the Saskatchewan Pork Producers Marketing Board registry. A swine farmer was defined as a person spending 2 h or more per day in an enclosed swine confinement building with an annual production of 700 or more swine per year for at least one year before the initial investigation in November 1989 .Producers who worked in open facilities or who raised swine on pasture land were excluded. The study subjects were producers or employees who allowed access to the swine facility during both study periods, and allowed environmental measurements to be taken on two occasions, once during the summer and once during the winter in each of the study periods, according to the study protocol. Subjects provided informed, written consent. The study protocol was approved by the University of Saskatchewan’s Advisory Committee on Ethics in Human Experimentation.