The amount of nitrogen (N) in clover dry matter (DM) herbage derived from N fixation in subterranean or white clover was estimated using the ¹⁵N enrichment technique in a dryland grazing experiment at Lincoln University. Clovers were established in separate mixed swards with cocksfoot in February 2002. Nitrogen fixation measurements were made between November 2002 and December 2005. Both clovers fixed 28 ± 0.7 kg N/t clover DM (R²=0.96). Using the 28 kg N/t DM reported here and previously published clover yields from the ‘MaxClover’ experiment in Years 1-7, N fixation averaged 81 kg N/ha/yr (range: 41-106 kg N/ha/yr) from subterranean clover and 46 kg N/ha/yr (range: 18-90 kg N/ha/yr) from white clover. Annually, total N fixed by subterranean clover exceeded that from white clover in 4 of the 7 years.