The present study was conducted to evaluate characteristics of pig houses that are associated with the development of respiratory morbidity in 100 swine producers with work-related respiratory symptoms. A standardized questionnaire for farm characteristics was used, and lung function was assessed immediately before and after feeding the pigs. Exposure to dust and endotoxin was determined by personal sampling. Among these farmers, baseline lung function results were shown to be negatively associated with duration of employment, number of pigs on the farm, manual feeding, and ventilation. The decrease in forced vital capacity and forced expiratory volume in 1 second over the feeding period was negatively correlated with air velocity, whereas respirable dust concentrations were shown to be significant predictors of maximal midexpiratory flow (MMEF25/75) decline. In conclusion, among symptomatic pig farmers, those with higher numbers of pigs and longer duration of employment are at highest risk for developing functional impairment.