Patients infected with the human immunodeficiency virus (HIV) suffer from serious and life- threatening infections. These patients often present with pyrexia but without localizing signs. Despite its high sensitivity in identifying focal infection67Ga citrate scintigraphy lacks specificity; lymphoma and solid tumours may also be imaged. This presents particular problems in HIV-positive patients with pyrexia where the differential diagnosis is often between infection and lymphoma. In an attempt to improve the specificity of radionuclide imaging in these patients a combination of67Ga citrate and the new agent99Tcm-labelled human immunoglobulin (99TCm-HIG) was used in 25 patients who were sequentially imaged with the two agents. Fourteen patients had 29 sites of microbiologically confirmed infection;67Ga citrate identified 27 sites and99Tcm-HIG identified 16 sites. Seven of the nine sites visualized with99Tcm-HIG, but positive with67Ga citrate, were intrathoracic. Abnormal concentration of67Ga citrate, not due to infection, occurred at eight sites; five lymphoma, one gout, one recent fracture and one patient with prominent bone marrow islands.99Tcm-HIG showed increased concentration of tracer in only one of the patients with lymphoma. A combination of67Ga citrate and99Tcm-HIG imaging in HIV-positive patients with pyrexia of unknown origin enables a differentiation between infection and lymphoma to be made more readily. The poor sensitivity of99Tcm-HIG in the chest will limit its sole use in this patient group. © 1991 Chapman and Hall Ltd.