Leghorn layers were monitored for heat loss, feed intake, egg production and respiratory rate at various environmental temperatures (TJ after first being exposed to aerial ammonia (NH3). The initial exposure was to 10 or 60 ppm NH3 at a T, of 25 °C for 30 days to simulate a winter environmental condition in a poultry facility. Hens were then allowed to recover in an environment of 5 ppm of NH3 at a T^ of 22 °C for seven days to simulate a spring environmental condition. Birds were then placed individually in a partitional calorimeter free of NH3 at 25, 29, 33, or 37 °C for 24 h to simulate initial summer environmental conditions. There were no statistical differences (P>0.05) between the two groups of NH3-treated hens for sensible or latent heat losses, apparent respiratory efficiency of latent heat loss, egg production, or feed intake. From these resutls, it is hypothesized that interplay between cutaneous evaporative heat loss and respiratory evaporative heat loss may play a more important physiological role than previously thought in maintaining homeothermy of the bird at high environmental temperatures. This physiological reponse could thus provide an energetics compensation for lung damage caused by aerial ammonia.