1. Non-demented HIV seropositive and seronegative methadone maintained patients and healthy volunteers (n = 10 each) participated. 2. All subjects underwent SPECT regional cerebral blood flow scanning following injection of Tc-99m HMPAO. All patients underwent neuropsychologic (NP) testing. 3. The left striatum/whole brain blood flow ratio was elevated in the HIV positive group compared to the healthy subjects. Two HIV positive patients had clearly abnormal striatal ratios. Both groups were impaired on NP testing; HIV+ patients were somewhat more impaired on tests of sustained attention and verbal memory. 4. SPECT scanning with Tc-99 HMPAO may identify a subgroup of HIV positive patients with evidence of CNS involvement prior to onset of dementia symptoms.