Nitrogen fertilizer taxes have been proposed as a means of controlling agricultural ‘over-production’ and nitrate pollution of water courses in the EC. This paper constructs time-series models of fertilizer demand which provide quantitative information relevant to this issue. Time-series data on the use of nitrogen fertilizer in UK agriculture is found to have a unit root with non-zero drift coupled with a one-time change in drift after testing against the alternative hypothesis that the process is trend-stationary with a break in trend. The stochastic component of the nitrogen use series is cointegrated with the ratio of the price of nitrogen fertilizer to the price of agricultural output. Appropriate error correction models are estimated. Both the short-run and long-run price elasticities of the response of nitrogen use are found to be rather low. Some brief policy conclusions are drawn.