The effect of nitrogenous fertilizer on a white clover sward was studied to obtain information to be used in the evaluation of white clover in grassland. There was no evidence of a yield response. The weight of nodules was depressed by the addition of fertilizer.Where management is adjusted to maintain white clover in swards receiving large quantities of nitrogenous fertilizer the clover may use part of this fertilizer at the expense of symbiotic fixation.The relation of the results obtained to the assessment of the benefit derived from white clover in mixed swards is briefly discussed.