B-C-N, C-N and B-N nanotubes, prepared by the pyrolysis of the appropriate precursor compounds around 1000°C in an atmosphere of argon, have been examined by electron microscopy and other techniques. The compositions of the nanotubes have been analysed by electron energy loss spectroscopy and X-ray photoelectron spectroscopy. There is significant compositional variation in B-C-N and C-N nanotubes. Properties of the B-C-N and C-N nanotubes have been compared with those of carbon nanotubes, particularly with respect to the I-V characteristics as obtained from UHV-STM studies. The near absence of B-N nanotubes on pyrolysing the appropriate precursor compound, and other observations made in the present study, indicate the crucial role played by carbon in the initial nucleation and growth of nanotubes.