The complete distribution of total soluble proteins was investigated in 40-year-old oak and beech trees, felled at two dates (October 1999 and June 2000), to estimate seasonal variations in protein content at tree level. The concentration of total soluble proteins was nearly twice as high in oak compared to beech (755 mg.g-1 Dry Mass vs. 4.2 mg.g-1 Dry Mass, respectively) and 10 times lower than total non structural carbohydrates. Scaling from samples to total tree biomass, the contribution of C stored as total soluble proteins accounted for 500 gC in oak trees and only for 250 gC in beech trees. The stem was the major storage compartment in both species. Soluble proteins made up most of nitrogen at the stem and roots of oaks, while in its branches and in all beech organs, several N compounds predominated. These concentrations varied before bud break and stem growth in oak and beech. The seasonal progression of total soluble proteins in twigs of both species showed opposite patterns, especially during Spring, probably due to internal redistribution of proteins from upper stem and large branches. The dates of minimum and maximum concentrations were different for total soluble proteins and total non structural carbohydrates.