A Study to Evaluate the Effect of Cimetidine on CD4 Lymphocyte Counts in HIV Infection

Inclusion Criteria: Concurrent Medication: Allowed: * All FDA-approved medications, antiretrovirals, and PCP prophylaxis drugs, with the exception of warfarin (Coumadin). * Other self-prescribed medications available either over the counter or through buyer's clubs. Patients must have: HIV positivity. NOTE: * Patients on an antiviral or immunomodulating drug must have received it for at least 2 months and have no intention to make clinical or therapeutic changes in the first 8 weeks (such as adding a new agent or discontinuing effective viral suppressive therapy) that may interfere with the study. NOTE: * Patients who become pregnant after enrollment will be permitted to continue on study drug but must sign an additional informed consent indicating their awareness of the issues in taking a drug with limited safety data during pregnancy. Prior Medication: Allowed: * Antiviral and immunomodulating drugs, provided patient has been on such therapy for at least 2 months prior to study entry. Exclusion Criteria: Co-existing Condition: Patients with the following symptoms or conditions are excluded: * Known intolerance or hypersensitivity to cimetidine. * Evidence of active opportunistic infection or malignancy requiring high-dose systemic chemotherapy. * Any symptoms suggestive of concurrent illness that are not attributable to overall impairment by HIV or are not diagnosable based on the available evidence. * Inability to swallow tablets (gastric feeding tubes are allowed). * Not willing to comply with visit schedule and study procedures. Concurrent Medication: Excluded: * Warfarin (Coumadin). Prior Medication: Excluded within 4 weeks prior to study entry: * cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), and nizatidine (Axid).