Dimers and codimers resulting from thermal cycloaddition reactions of 1,3-cyclopentadiene, isoprene, cis-1,3-pentadiene and trans-1,3-pentadiene were characterised in terms of their Kovats retention indices on a HP-PONA capillary column at 100°C. The proportion of individual isomers in dimerisation andcodimerisation products under defined reaction conditions and their chromatographic characteristics were compared with published data. The chemical structure of isomer products was assigned on the basis of agreement between experimental and literature data.