Evidence derived from studies concerning brain metabolism and brain electrical activity suggests that temporal lobe functioning is impaired in the course of HIV infection. To test the hypothesis of temporal lobe dysfunction in HIV infection, we utilized computerized electroencephalogram (EEG) analysis to evaluate temporal lobe EEG power modifications induced by olfactory stimulation in 10 HIV-infected patients as compared with 10 seronegative control subjects. Our findings show that HIV-infected patients respond to olfactory stimulation with an increase in temporal lobe slow electrical activity (theta EEG power), whereas control subjects show a decrease in the same activity. The theta EEG power increase during olfactory stimulation in HIV-infected patients can be interpreted as a paradoxical response of the deep temporal regions to specific procedures, supporting the hypothesis of temporal lobe dysfunction in HIV infection.