L-[Me-13C]-Methionine, sodium [2-13C]acetate and sodium [1,2-13C]acetate were incorporated into destruxins A, B and E by the entomopathogenic fungus Metarhizium anisopliae. NMR analysis established that methionine is involved in the N-methylation of L-valine and L-alanine, and that one intact acetate unit participates in the biosynthesis of the -CH(OH)-COOH fragment of the hydroxy acid moiety. The presence of two acetate units in proline and isoleucine agrees with the accepted biochemical schemes.