 This study will determine whether blood levels of the anti-HIV medicine nevirapine are different in HIV-infected patients in the United States from patients in Uganda. People from all over the world take medications to treat HIV infection. These medicines work well in some people but not in others, and they cause harmful side effects in some people and not in others. These differences may be related to variations in how much of the drug reaches the blood. Differences in drug blood levels among people in various areas of the world may be attributed to differences in diet, state of health, ability to absorb the medicines from the stomach, ability to eliminate the drugs from the body, and the brand of medicine taken. This study will help scientists learn whether differences in blood levels of HIV medicines are important in determining how well the drugs work in different patient populations. 