Pyrolysis-hydrogenation-GLC has been applied to copolymers of ethylene with propylene and butene-1, to propylene-butene-1 copolymers and to partly unsaturated ethylene-propylene terpolymers. Copolymers of ethylene with up to about ten per cent by weight of butene-1, hexene-1 and octene-1 have been used to interpret the pyrograms of Ziegler, and of high-pressure, polyethylene. The method is shown to provide information both about the composition and about the structure, degree of alternation, head-to-head or head-to-tail arrangement, etc., of copolymers. Quantitative methods of analysis are described for ethylene-propylene copolymers and for ethylene-propylene-dicyclopentadiene terpolymers.