[3-14C]Phenylalanine has been administered to Derris elliptica. The isolated rotenone has 87% of its radio-activity located at C-6a, in accordance with the 1,2-aryl shift previously reported. [Me-14C]Methionine has been fed to Derris elliptica plants, and germinating seeds of Amorpha fructicosa. In both cases the isolated rotenoid was labelled almost entirely at C-6 and the methoxy-groups. In the former case, C-6 of rotenone was supplied to the extent of 0·47–0·51 times the mean figure for a methoxy-group. Similar results (0·50–0·68) were obtained for amorphigenin in the second case.