Double-Blind Study of Timunox (Thymopentin) in Asymptomatic HIV-Infected Patients Receiving Either Mono (AZT or ddI) or Combination (AZT / ddI or AZT / ddC) Anti-Retroviral Therapy

Inclusion Criteria Patients must have: * Asymptomatic HIV infection. * CD4 count 100-400 cells/mm3. * No HIV-associated neurologic abnormalities or constitutional symptoms. * No oral hairy leukoplakia. * At least 6 months of prior AZT. Exclusion Criteria Co-existing Condition: Patients with the following symptoms or conditions are excluded: * Abnormal chest x-ray, consistent with active opportunistic infection. * Hypersensitivity to thymopentin. * Significant chronic underlying medical illness. * Grade 2 or worse peripheral neuropathy. Concurrent Medication: Excluded: * HIV vaccines. * Investigational or non-FDA approved medication. * Immunomodulatory therapies. * Experimental therapies. * Any antiretroviral therapy other than AZT, ddI, ddC, d4T, or 3TC. Patients with the following prior conditions are excluded: * Herpes zoster (within the past year). * Recurrent (\> one episode) oral candidiasis (confirmed). * Vulvovaginal candidiasis (persistent, frequent, or poorly responsive to therapy). * Bacillary angiomatosis. * Listeriosis. * Idiopathic thrombocytopenia purpura. Prior Medication: Excluded at any time prior to study entry: More than one dose of thymopentin. Excluded within 30 days prior to study entry: * HIV vaccines. * Investigational or non-FDA approved medication. * Immunomodulatory therapies. * Experimental therapies. * Any antiretroviral therapy other than AZT, ddI, ddC, d4T, or 3TC. Required: * Prior AZT (\>= 300 mg/day) for at least 6 months; on current regimen (any combination of approved nucleoside analogues) for at least 4 weeks. Significant active alcohol or drug abuse.