The capability of acetylene and carbon mononide of forming intermediate compounds with inclusion components, because of their significance as starting materials for many syntheses, was studied by means of a newly developed apparatus along with the use of C14O and acetylene-C14. The studies showed that carbon monoxide did not yield an inclusion system or inclusion compound with any of the substances studied and that acetylene gave a labile inclusion compound only with [alpha]-dextrin. In testing the technique of investigation it was established, moreover, that mesoheme in the absence of pyridine takes up two moles, mesoheme-poly-DL-(phenylalanine-glutamic acid) in the presence of pyridine takes up one mole of CO and that CO compounds of the Cu, Ni, and Co complexes of the proto- and mesoporphyrin IX are not detectable.