Normal volunteers 18 years of age and older may enroll in Part 1 of the study. HIV-infected patients 18 years of age and older who have not previously been treated with a NNRTI (efavirenz, nevirapine, and delavirdine) may participate in Part 2. All prospective study participants will be screened for eligibility with a physical examination, blood tests, a urine test and an electrocardiogram (ECG).