Pre-emergence application of metribuzin stimulated the accumulation of nitrogen, especially in the form of protein. The application of metribuzin induced marked suppression of carbohydrates. The soluble sugars and polysaccharides in nontreated control plants declined throughout the experimental period. The inhibitory effect of metribuzin on carbohydrates was concomitant with changes in photosynthetic efficiency, biosynthesis of pigments (chlorophyll), and the nucleic acid contents. The chlorophyll a/b ratio was not affected by metribuzin application.