Blood Levels of Abacavir After One Dose in HIV-Infected Children and Adolescents

Inclusion Criteria Patients may be eligible for this study if they: * Are 9 to 18 years of age. * Are HIV-positive. * Have a CD4 cell count above 200 cells/microL. * Have a viral load (level of HIV in the blood) under 100,000 copies/ml. * Have not changed their anti-HIV drugs for the 4 weeks before study entry. * Are able to swallow study medications. * Both males and females, agree to use a barrier method of birth control for 3 days after taking the abacavir dose for this study. (This study has been changed. In the earlier version, no birth control was needed.) * Can be followed at a participating Pediatric AIDS Clinical Trials Unit (PACTU) for the entire study. * Provide written consent of a parent or guardian, if under 18 years of age. Exclusion Criteria Patients will not be eligible for this study if they: * Have liver or kidney problems, as shown by screening tests. * Have medical or surgical problems that affect movement or absorption in the stomach or gut. * Have an opportunistic (AIDS-related) or serious bacterial infection requiring medicine at the time of enrollment. * Have any diseases (other than HIV infection) or other findings that, in the investigator's opinion, might make it harmful for the patient to be on the study. * Have a history of chronic alcohol use. * Fall outside of a certain weight range for their age. * Are pregnant or breast-feeding. * Are receiving or have received abacavir. * Are receiving nonnucleoside reverse transcriptase inhibitors, including efavirenz, delavirdine, or nevirapine; hydroxyurea; mycophenylate; rifampin, rifabutin, anticonvulsants, or other drugs that affect the liver; or chemotherapy for active cancer. * Have received interferons, interleukins, HIV or other vaccines, or experimental therapy within 30 days before entering the study.