Data of two field experiments, in which the nitrogen application rate was varied between 0 and 300 kg/ha, were used to analyze the factors that affect marketable yield in Brussels sprouts. Marketable yield (Y) is a function of radiation use efficiency (RUE), cumulative intercepted radiation (IPAR), partitioning of biomass (P) and the dry matter concentration in the buds (DMC): Y=RUE*IPAR*P/DMC. The effect of nitrogen application rate on marketable yield was analyzed in these terms. RUE was not affected by nitrogen application rate. Nitrogen application rate had also only a small effect on P and DMC. The effect of nitrogen availability on IPAR was the key factor in determining marketable yield. It had a strong effect on canopy development resulting in increasing interception of incoming radiation at higher nitrogen application rates. Consequences for cultural measures to obtain maximum yield are discussed.