Children have been receiving medications to prevent complications of HIV infection, such as Pneumocystis carinii pneumonia (PCP), Mycobacterium avium complex (MAC) disease, or other bacterial infections. It is common for HIV-positive patients with low CD4 counts to receive these preventive medications. However, these drugs can have serious side effects, they are expensive, and it is possible for bacteria resistant to the drugs to grow. For these reasons, it may be beneficial to the child to stop taking these preventive medications if he/she has been on anti-HIV (antiretroviral) therapy and has improved CD4 counts. This study will look at how many children who stop taking their medications develop opportunistic infections.