Drainage and urea fertilization of forested peatlands in western Canada are being contemplated as means for increasing peatland conifer productivity. Surface application of urea-based fertilizers may result in loss of some N by volatilization of NH 3. The objective of the present study was to assess the loss of NH 3 from undrained and drained peatland sites as affected by various N dosages, i.e. 0 (unfertilized), 200 (N 2) and 400 kg N ha −1 (N 4), following field broadcast application of urea fertilizer. Losses of NH 3 from fertilized plots were higher on the undrained relative to the drained site. Increase in urea-N dosage increased NH 3 volatilization from both sites. Most of the NH 3 volatilization losses occurred during the first 9 days after fertilizer application. The precipitation that occurred on day 9 after fertilizer application decreased NH 3 volatilization to background levels of unfertilized plots for the rest of the study period. Net mean losses of NH 3 from the undrained site were 3% and 4% of applied N for N 2 and N 4, respectively. Corresponding losses on the drained site were 0.7% and 7%. These magnitudes of loss of N appear to be less important from a forest management point of view.