The purpose of this study is to look at the safety and effectiveness of receiving lamivudine (3TC) once a day versus twice a day as part of an anti-HIV drug combination.

Patients are randomized to receive the same total dosage of 3TC either twice a day (Group 1) or once a day (Group 2) in combination with ZDV and EFV over 48 weeks. Viral load measurements will be performed at Weeks 4, 8, 12, 16, 20, 24, and every 8 weeks thereafter.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are 18 years of age or older.
• Are HIV-positive.
• Have a viral load (level of HIV in the blood) of at least 400 copies/ml within 21 days of study entry.
• Have a CD4 count greater than 100 cells/mm3 within 21 days of study entry.
• Agree to practice abstinence or use effective barrier methods of birth control (or, if patient is a woman, unable to have children).

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have taken any antiretroviral (anti-HIV) agent.
• Are pregnant or breast-feeding.
• Are unable to absorb food or have trouble taking medicines by mouth.
• Abuse alcohol or drugs to an extent that may make study participation difficult.
• Are not likely to be able to complete the 48 weeks of study treatment.
• Have a history of pancreatitis (inflamed pancreas) or hepatitis within the last 6 months or any evidence of liver disease.
• Have received an investigational vaccine within the past 3 months or have received gene therapy.
• Have a severe medical condition such as diabetes or heart trouble.
• Have been diagnosed with AIDS.
• Have had radiation therapy or chemotherapy within 30 days of study entry, except for treatment of Kaposi's sarcoma.
• Are taking medications that affect the immune system within 30 days of study entry.
• Are taking medications that may interact with the study drugs.