All patients must receive treatment with antiretroviral nucleosides in addition to study treatment. Patients are randomized equally into 1 of 3 outpatient dosage groups. Group 1 receives placebo; Group 2 receives a low dose of Procysteine; and Group 3 receives a higher dose of Procysteine. Patients receive study treatment for 6 months (total duration of patient participation is 30 weeks).