To evaluate the antiretroviral activity and safety of 200 mg BID and 300 mg BID doses of MPC-4326 administered as monotherapy for 14 days to HIV-1 positive patients. Patients with an initial treatment response will have the option to continue MPC-4326 in combination with an Optimized Backround Regimen for a maximum of 72 weeks.

Inclusion Criteria:

• Be at least 18 years of age at the time of screening.
• Have HIV-1-infection.
• Have a CD4+-lymphocyte count≥100 cells/mm3
• Have a screening plasma HIV-1 RNA value, measured by the Roche Amplicor assay, of 2,000 - 500,000 copies/mL (inclusive).
• Be free from any acute infection or serious medical illness within 14 days prior to study entry.

Exclusion Criteria:

• Current opportunistic infection characteristic of AIDS (Category C according to the CDC Classification System for HIV-1 Infection, 1993 Revised Version, Appendix A) that is diagnosed within 30 days or is poorly controlled.
• Patients with systolic blood pressure < 90 mmHg or > 140 mmHg or diastolic blood pressure < 60 mmHg or > 90 mmHg.
• A history of seizures (excluding pediatric febrile seizures) or current administration of prophylactic anti-seizure medications.
• A history of cerebrovascular accident (CVA) or transient ischemic attacks (TIA).
• Patients with the following laboratory parameters within 30 days prior to first dose of study drug: Hemoglobin < 10.0 g/dL for men and < 9.0 g/dL for women Neutrophil count < 1000/mm3 Platelet count < 50,000/mm3 AST or ALT > 2.5 times the upper limit of normal (patients with a positive HBV surface antigen or HCV antibody test at screening must have AST and ALT no more than 1.5 times the upper limit of normal)