The ommochrome dyestuff Xanthommatin (I) previously isolated from the secretions of Vanessa urticae was isolated in pure form from the eyes of the blowfly Calliphora erythrocephala.It was shown by means of injection of radioactive labelled tryptophan (II) in Calliphora pupae and estimation of the radioactivity of the Xanthommatin extracted from the newly hatched flies that the ommochrome Xanthommatin is a final product of the tryptophan metabolism.