Intensification of poultry housing systems and the need to maintain a high ambient temperature have resulted in an atmosphere that is polluted with ammonia, hydrogen sulphide, carbon dioxide, dust particles and endotoxins. This experiment was carried out to determine if broiler fowl, when given a free choice, would avoid ammoniated environments. The effect of rearing aerial environment on these preferences was tested subsequently during a similar free choice experiment. Firstly, the birds were given a free choice of 4, 11, 20 and 37 ppm atmospheric ammonia over a period of 16 days. Data were collected in two different light levels (bright or dim light). The birds avoided the two higher ammonia concentrations, choosing to spend equal amounts of their time in 4 and 11 ppm during the bright phase. During the dim period, broiler fowl spent more time in 4 ppm. Secondly, broiler fowl were exposed to either 2 or 19 ppm ammonia from 1 to 26 days of age. Following this, the birds were given a choice of compartments containing 4, 12, 20 and 37 ppm of ammonia. Birds again avoid the two higher concentrations of ammonia. In summary, broiler fowl avoid ammonia at concentrations commonly found on poultry units regardless of previous experience, suggesting that it to be aversive at concentrations above approximately 10 ppm.