The incorporation of L-methionine- (methyl-14C) into isoflavones of young chana plants (Cicer arietinum L.) of various age was determined. The percent incorporation into biochanin A was highest in 7 day old plants and decreased with the age of the plants whereas the incorporation into formononetin remained fairly constant. The data provide further evidence for a turnover of formononetin. By simultaneous pulse labelling with L-methionine- (methyl-3H) and DL-phenylalanine- (1-14C) it could be shown that isoflavones are not subject to demethylation reactions. The results also demonstrate that the enzymes necessary for the formation of isoflavones and the metabolism of formononetin are qualitatively and quantitatively built up in young plants.