To compare effects on CD4 counts and serum viral RNA among HIV-seropositive, zidovudine (AZT)-experienced patients in three treatment arms: indinavir sulfate ( MK-639; Crixivan ) plus AZT plus lamivudine ( 3TC ) versus MK-639 alone versus AZT/3TC.

AZT-experienced patients are randomized to receive MK-639/AZT/3TC or MK-639 alone or AZT/3TC. Additionally, patients who have received < 6 months of AZT or who are intolerant but received prior 3TC or who require concomitant rifampin therapy may receive open-label MK-639.

Inclusion Criteria

Concurrent Medication:

Allowed for all patients:

• Standard prophylaxis for opportunistic infections.
• Continuation of treatment for opportunistic infection.

Allowed for open-label study patients:

• Rifampin.

Patients must have:

• HIV positivity.
• CD4 count <= 50 cells/mm3.
• More than 6 months of prior AZT (blinded study only).

NOTE:

• Patients on the open-label study must have AZT intolerance or have < 6 months of prior AZT.

Prior Medication:

Required for blinded study patients:

• > 6 months of prior AZT.

Required for open-label study patients:

• < 6 months of prior AZT.

Allowed for open-label study patients:

• Prior 3TC.

Exclusion Criteria

Concurrent Medication:

Excluded in all patients:

• Immunosuppressants.

Excluded in blinded study patients:

• AZT, ddI, ddC, or d4T.
• Rifampin.

Excluded in open-label study patients:

• 3TC.

Prior Medication:

Excluded in all patients:

• Prior protease inhibitors.
• Investigational agents and immunomodulators within 30 days prior to study entry.
• Immunosuppressants within 2 weeks prior to study entry.

Excluded in blinded study patients:

• Any prior 3TC.
• AZT, ddI, ddC, or d4T within 2 weeks prior to study entry.

Excluded in open-label study patients:

3TC within 30 days prior to study entry.