The proximate analysis of the cod parasite,Porrocaecum decipiens, has been carried out. During the determination of the amino acid composition of a hydrolysate of the parasite the presence of an unusual complex was detected as an unknown peak in the amino acid ion-exchange chromatogram. The unknown complex was also found to be present in a protein-free nucleic acid fraction prepared from the parasite. The substance proved to be highly resistant to conventional methods of hydrolysis. Glutamic acid was found to be an end product when the complex was degraded and it is thought that the complex consists of a thymine nucleoside associated with a peptide consisting of three to five glutamic acid residues. It is not known whether the complex is naturally occurring or is an artifact formed during the acid hydrolysis.