Inclusion Criteria

Concurrent Medication:

Allowed:

• Chronically administered concomitant therapies for HIV and opportunistic diseases, including chemotherapy for cutaneous Kaposi's sarcoma, must be on these therapies for at least 30 days prior to study entry.
• Short courses of oral antibiotics or other therapies given for a limited period of 3 weeks.
• Episodic use of IV acyclovir or oral acyclovir > 1g/day for treatment of acute illness is permitted at the clinician's discretion.

Patients must have:

• A working diagnosis of HIV infection based on the patient's medical history, behavioral history, clinical signs and symptoms, or results of other laboratory tests.
• CD4+ cell count <= 100 cells/mm3 within 60 days prior to randomization (OR, AS PER AMENDMENT 8/7/97, a CD4+ cell count that is both > 100 and <= 200 cells/mm3 within 60 days prior to randomization and a documented nadir CD4+ cell count <= 50 cells/ mm3 at any time prior to randomization).
• Reasonably good health.
• Life expectancy of at least 6 months.
• Access to a refrigerator for the storage of adefovir dipivoxil.
• Signed informed consent from parent or legal guardian for patients less than 18 years of age.

AS PER AMENDMENT 8/7/97:

• CMV serology (IgG) positive (CMV bDNA cohort and CMV-virology cohort).

Exclusion Criteria

Co-existing Condition:

Patients with the following symptoms and conditions are excluded:

• Evidence of active CMV disease at screening.
• Conditions that would require use of medications listed in Exclusion Concurrent Medications.

Concurrent Medication:

Excluded:

• Any investigational anti-CMV agent.
• Adenine arabinoside (vidarabine).
• Amantadine hydrochloride (Symmetrel).
• Cidofovir (Vistide).
• CMV hyperimmune globulin.
• Cytosine arabinoside (cytarabine).
• Famciclovir.
• Foscarnet (phosphonoformic acid).
• Ganciclovir (Cytovene).
• GW 1263W94 (Benzamidazole).
• Idoxuridine.
• Intravenous acyclovir.
• ISIS 2922 (Anti-sense).
• Lobucavir.
• MSL109.
• Oral acyclovir > 1 g/day.
• Valacyclovir.

Patients with the following prior conditions are excluded:

• History of CMV end-organ disease.

Prior Medication:

Excluded within 2 weeks of randomization:

• Any investigational anti-CMV agent.
• Adenine arabinoside (vidarabine).
• Amantadine hydrochloride (Symmetrel).
• Cidofovir (Vistide).
• CMV hyperimmune globulin.
• Cytosine arabinoside (cytarabine).
• Famciclovir.
• Ganciclovir (Cytovene).
• GW 1263W94 (Benzamidazole).
• Idoxuridine.
• Intravenous acyclovir.
• ISIS 2922 (Anti-sense).
• Lobucavir.
• MSL109.
• Oral acyclovir > 1 g/day.
• Valacyclovir.

Excluded within 60 days prior to study entry:

• Foscarnet.