Bone marrow cellularity may be assessed from the water-lipid spectra provided by proton (1H) magnetic resonance spectroscopy. The sequence used for this technique on an MR scanner is described in this article. The results obtained in 18 healthy volunteers and 15 patients with different vertebral marrow abnormalities are presented. Accurate localisation with the aid of an appropriate phantom is essential. Focal bone marrow abnormalities were difficult to study due to partial volume artefacts. Conversely, in cases of diffuse bone marrow disease, the assessment of marrow cellularity by MR spectroscopy gave results comparable to those from the bone biopsy.