Methods using conventional Fourier transform 1H n.m.r. spectroscopy at 250 MHz for the determination of the overall deuteration levels of cells cultured in media containing 2H2O or deuterated carbon sources are described. These were developed for Escherichia coli as a model, and extended to Neurospora crassa hyphae and mouse myeloma cells P815. The results were investigated by 1H n.m.r. and neutron scattering measurements on deuterated proteins that were obtained from E. coli. It is concluded that 1H n.m.r. is able to observe the soluble proteins of E. coli in certain cases, that deuteration levels can be determined by 1H n.m.r. for small quantities of proteins in their native state, and that glycerol is a more efficient carbon source than glucose for the deuteration of E. coli proteins.