Ammonia volatilization from urea-treated soils was estimated under field and laboratory conditions. Acid-washed filter papers were hung in the air in a spruce stand treated with N and P fertilizers in a factorial design. In the laboratory, moss sods were incubated to quantify ammonia volatilization. Ammonia volatilization increased with the level of N applied and more ammonia was absorbed by filter papers at 0.6 m above the ground than those at 1.2 m. Maximum rates of ammonia volatilization in urea-treated plots were observed between the third and fourth day after fertilizer application and similar absorption patterns were observed in areas not treated with urea. It is, therefore, suggested that ammonia volatilized from urea-treated plots can move to untreated areas. Addition of P along with urea significantly reduced ammonia volatilization under field conditions. Laboratory experiments showed that addition of urea to moss sods increased the pH of the organic layer from about 3.6 to 8.8. Sphagnum moss sods volatilized more ammonia (about 1.7 per cent of the added material) than feather moss sods (about 0.8 per cent). At higher incubation temperatures, however, the rate of ammonia volatilization decreased in sphagnum moss sods but increased in feather moss sods.