Several small-molecule hosts form inclusion compounds (ICs) with polymers. In these ICs the guest polymer chains are highly extended and isolated from neighbouring polymer chains by the clathrate wall. Only polymers with extended conformations are narrow enough to reside in the narrow channel. An inclusion compound has been formed between urea and trans-1,4-polyisoprene (TPI) and investigated using FTi.r. spectroscopy. Infrared bands observed for this IC indicate that the crystal structure of this IC is most likely different from the usual hexagonal. crystal structure. It is also suggested that TPI in the channel adopts a conformation which is similar to bulk TPI with beta crystal modification.