Central nervous system involvement is increasingly being recognised as a common manifestation of the acquired immunodeficiency syndrome (AIDS), either as a direct effect of the human immunodeficiency virus, or as a result of secondary infection or malignancy. A subset of patients with clinical or psychometric evidence of CNS involvement have normal appearances on imaging. This report describes proton magnetic resonance spectroscopy (1H MRS) in two patients with AIDS and discusses the role of 1H MRS in providing a marker of neuronal loss in patients with normal or borderline imaging.