a b s t r a c tBroiler husbandry is a significant source of ammonia (NH 3 ), nitrous oxide (N 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) emissions but scarce studies have been made under Mediterranean conditions. The aim of this study was to evaluate the NH 3 , N 2 O, CO 2 and CH 4 emissions on commercial broiler houses under Portuguese winter conditions. The study was made on a commercial broiler farm located in central Portugal. Three tunnel ventilated broiler houses with similar equipment and production practices were selected. The outdoor and indoor environmental conditions, gas concentrations and ventilation rates of each broiler house were measured during 42 days of growing cycle. Results showed that the maximum concentrations of NH 3 , N 2 O, CO 2 and CH 4 did not exceed the threshold values recommended to maintain indoor air quality on broiler houses. The average emission rates from broiler houses under winter conditions were 0.13 ± 0.04, 0.041 ± 0.002, 96.2 ± 8.8 and 0.226 ± 0.013 g day À1 bird À1 (22.0 ± 7.3, 6.7 ± 0.3, 16,028 ± 1465 and 37.7 ± 2.1 g day À1 LU
À1) for NH 3 , N 2 O, CO 2 and CH 4 , respectively. Furthermore, NH 3 and N 2 O emission rates of this study are in the same range than measurements from most European countries, but CH 4 emission rate seems higher to those reported for Mediterranean countries.