The purpose of this study is to determine any adverse effects of PRO 542 after administration and to determine the anti-HIV effects of PRO 542 in the patient.

A 2 arm study involving a series of 3 triweekly doses of PRO 542. One arm will involve patients on a stable dose of anti-retroviral therapy and the other arm will consist of patients not receiving anti-retroviral therapy. Three patients will be enrolled in each arm followed by a safety evaluation. Following the safety evaluation, 3 more patients may be enrolled in each arm. After the first 12 patients, an additional 12 patients may be enrolled pending safety data.

Inclusion Criteria:

• Confirmed diagnosis of HIV
• Patients must be on a stable dose of acceptable anti-HIV therapy or receiving no anti-HIV therapy for at least four (4) weeks prior to the start of this study
• HIV-1 determination by RNA-PCR greater than or equal to 100,000 copies/ml
• CD4 count >50/cubic mm at screening

Exclusion Criteria:

• Patients who have previously received PRO 542
• Patients with active, significant infection (other than HIV) not controlled by antibiotics
• Pregnant or lactating women
• Patients with an estimated life expectancy of <3 months
• Patients currently receiving steroids or other immunosuppressive therapy or immunoglobulin therapy except for topical or inhaled steroids
• Patients with known allergy or hypersensitivity to PRO 542 or immunoglobulin preparations