Seasonal change in foliar nitrogen concentration was determined in samples of Alnus glutinosa leaves gathered at intervals of 4 weeks from late May until November just prior to leaf fall in a mixed plantation of A. glutinosa and Juglans nigra in southern Illinois. The seasonal pattern of Alnus leaf nitrogen concentration was different from that reported for other winter-deciduous trees, which have relatively high nitrogen concentrations in spring and trans-locate considerable portions of their leaf nitrogen to nearby twigs and branches prior to leaf fall in autumn. Foliar nitrogen concentration of Alnus was low in the spring, then rose, remaining at a stable level of about 3 percent throughout the summer, and decreased very little during autumn. The autumnal decrease in Alnus leaf nitrogen concentration was only 16 percent compared with reported average values of from 33 to 66 percent for other winter-deciduous tree species. Sample time contributed significantly to the total variation in Alnus leaf nitrogen concentration (α = 0.01), but leaf size class and interaction between leaf size class and sample time did not. A. glutinosa in this mixed plantation seemed to conserve nitrogen less effectively than other winter-deciduous tree species for which published accounts exist. Forest Sci. 27:239-243.