Summary. The strategic application of nitrogen (N) fertiliser on temperate pasture is a popular management tool for boosting pasture production, particularly when low soil temperatures limit clover-derived N availability. The responsiveness of a perennial ryegrass and white clover pasture to increasing rates of N fertiliser (0, 15, 30, 45 and 60 kg N/ha), applied as a single application, was investigated for 5 pre and 5 post mid winter N application dates. The trial was laid out in a randomised split-plot design, replicated 4 times, with N application date in the whole plots and N fertiliser rate in subplots. Herbage yields were estimated by mowing small plots, with animals excluded for the duration of a single regrowth period on each plot. The data are presented as averages for the 5 pre and 5 post mid winter responses separately, as the means of the pre and post winter partitions were significantly (P0.05) increases in dry matter yield were noted between the 45 and 60 kg N/ha rates in all but one response, consistent with diminishing returns. The efficiency with which N fertiliser was utilised ranged between 9.0 and 15.9 kg N dry matter/kg. Nitrogen efficiency was consistently lower at the 60 kg N/ha rate than for lower rates of N fertiliser. The application of N fertiliser increased pasture dry matter yields by between 582 and 703 kg dry matter/ha. Based on the 1997 cost of urea, the additional forage produced cost between 6.4 and 10.1 cents/kg dry matter. The data are reviewed in terms of the potential for strategic N fertiliser applications during the winter, while still maximising utilisation of clover-derived N during the warmer months.