To determine the safety, tolerance, and pharmacokinetics of a new improved microparticulate suspension formulation of atovaquone administered at one of two dose levels (per 09/30/94 amendment, a third dose level was added) daily for 12 days in HIV-infected and perinatally exposed (per 8/9/95 amendment) infants and children who are at risk of developing Pneumocystis carinii pneumonia (PCP).