To investigate seasonal effects on nodulation of legumes during an English summer, plants of Pisum sativum and Phaseolus vulgaris were sown in pots in the open at intervals of 14 days between March and July and the pots were watered on all days when rain did not fall. The weight of nodules per plant varied significantly between sowing dates and showed seasonal trends in both legumes, but in different directions. In P. sativum nodulation was at a minimum at the midsummer sowing date but with P. vulgaris the mid-summer sowing gave maximum nodulation. The data are further analysed in terms of number and size of nodules, and nodule weight as a percentage of plant weight.