The purpose of this study is to look at the safety and effectiveness of a pill called Trizivir that is a combination of three anti-HIV drugs (zidovudine, lamivudine, and abacavir). Zidovudine and lamivudine are often given combined in one pill (Combivir). In this study, Trizivir will be compared to Combivir plus abacavir.

Patients are randomized to receive either the triple combination tablet (Trizivir) or to receive Combivir plus abacavir as a separate tablet. Patients take their study medications for 24 weeks.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are at least 18 years old.
• Are HIV-positive.
• Are currently receiving one of the following anti-HIV drug combinations: Combivir plus abacavir, Combivir plus abacavir plus a protease inhibitor, or Combivir plus abacavir plus a non-nucleoside reverse transcriptase inhibitor (NNRTI). Patients must have been taking this drug combination for at least the past 16 weeks. This also must be the first anti-HIV drug combination the patient has received.
• Have a viral load (level of HIV in the blood) less than or equal to 400 copies/ml.
• Have CD4+ cell count greater than 200 cells/mm3.
• Agree to use effective methods of birth control.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have been diagnosed with AIDS.
• Have a gastrointestinal disorder that makes it difficult for patients to absorb food or to take medications by mouth.
• Have hepatitis.
• Have a serious medical condition, such as diabetes, congestive heart failure, or other heart disease.
• Are allergic to any of the study drugs.
• Abuse alcohol or drugs.
• Will not be available for the entire 24-week study period.
• Are pregnant or breast-feeding.
• Have taken or will need to take certain medications, including radiation therapy, chemotherapy, drugs that affect the immune system (such as interleukin), an HIV vaccine, foscarnet, and hydroxyurea.
• Are enrolled in another experimental drug study.