The grain yield and contents of the quantitatively predominant nutritional constituents of barley grain were determined in nine adapted spring barley varieties each grown at seven European locations with three or four replications. The largest variation in nutritional composition was due to different environmental conditions, but genotypic effects were also present. Interactions between genotype and environment were small. The average protein content at different locations varied from 8.1 to 14.7 per cent of the grain dry matter, and was not simply related to the amount of fertilizer-N applied. The nutritional composition of the grain was influenced by the grain yield level. The percentage of dietary fiber and protein decreased with increasing grain yield, but some varietal differences which were independent of the grain yield level could be established. The protein quality depended upon the protein level, as the protein contained more prolamin relatively to non-prolamin protein at high than at low protein levels. A difference between two varieties in the prolamin/non-prolamin ratio was consistent over a wide range of variation in protein content.