The effects of ventilation rate on air quality were investigated in 2 experiments, one with reduced ventilation and one with a cold air draught. Carbon dioxide, ammonia, hydrogen sulphide, particulate and microorganism levels were monitored and av. daily gain and feed to gain ratio were measured. Although contaminant concentrations were affected by different ventilation rates, piglet performance was not significantly different. No clinical pig health differences were observed although in the draught experiment piglet antibody response suppression indicated that these animals were stressed.