Twenty-seven groups of pigs of three each were raised in controlled-environment houses for 12 to 14 weeks. Three levels of humidity (% RH) were compared at temperatures of 22°, 28° and 33°C. Rate of gain and feed consumption decreased with increasing humidity at any of these temperatures, with effect of humidity increasing with increasing temperature. The rate-of-gain data were consistent with rates predicted from analysis of the effect of humidity on evaporative heat loss with respiration. Humidity had little effect on feed efficiency, rectal temperature, or skin temperature.