In New Zealand, the demand for nitrogen fertiliser has increased markedly since the early 1980s. Potentially, this trend has significant environmental and climate change implications. While many factors could contribute to this trend, little work has been done to examine the drivers of increased use of nitrogen fertiliser in New Zealand. In this paper, we review the international literature and discuss a theoretical framework for modelling fertiliser demand. Using a national data set, we develop an empirical cointegration model for New Zealand. The results suggest that, in the long run, nitrogen fertiliser use is elastic (2.3) to output prices and unit elastic to its own price.