In field trials in 1968-9, spring barley was sown after application of simazine at 0.25, 0.5, 1.0 or 2.0 kg/ha. Grain N and amino-acid contents were determined at harvest. The proportions of N compounds changed and there was an increase in total N and in extracted proteins in the grain following all simazine treatments, compared with untreated controls. Albumin and globulin levels were lower and prolamine content higher. A general decrease in essential amino acids was observed.