A nanocomposite of polypyrrole/carbon nanotubes prepared by in situ chemical polymerization shows improved conductivity of the polypyrrole as compared with its pure form. Its application as a chemical sensor, made using a simple spin-casting technique, shows a drastically increased sensitivity. The Figure shows a field-emission scanning electron microscopy (FE-SEM) image of the SWNT/Ppy nanocomposite.