This open-label study will evaluate the safety, pharmacokinetics and antiviral activity of a modified Invirase (saquinavir)/ritonavir regimen in treatment-naïve HIV-1 infected patients. Patients will receive Invirase 500 mg plus ritonavir 100 mg twice daily orally for the first week, followed by Invirase 1000 mg plus ritonavir 100 mg twice daily orally for the second week. The study treatment will be given in combination with two Nucleoside Reverse Transcriptase Inhibitors (NRTIs), in accordance with the current clinical HIV treatment guidelines. Anticipated time on study treatment is 14 days.

Inclusion Criteria:

• Adult patients, >/= 18 years of age
• HIV-1 infection
• Currently treatment-naïve and eligible to initiate a ritonavir-boosted Protease Inhibitor based regimen and willing and able to initiate saquinavir/ritonavir therapy for the first 14 days; the saquinavir/ritonavir regimen will be in combination with two Nucleoside Reverse Transcriptase Inhibitors (NRTIs), in accordance with the current clinical HIV treatment guidelines
• Body mass index 18-32 kg/m2, inclusive
• Female patients of childbearing potential and male patients with female partners of childbearing potential must use 2 methods of contraception as defined by protocol during the study and for at least one month after the last dose of study drug
• Non-smoker or patients who have stopped smoking more than three months prior to Day 1 of the study

Exclusion Criteria:

• Coinfection with hepatitis B or C (acute or chronic)
• Anticipated use or need for significant concomitant medical treatment during the study period, other than background antiretroviral therapy
• Participation in a clinical study with an investigational drug or device within 3 months prior to Day 1 of the study
• Pregnant or lactating women
• Any clinically relevant history of substance abuse or addiction including alcohol and/or other drugs of abuse
• Special dietary restrictions that would prohibit consumption of standardized meal (e.g. vegetarian, vegan, gluten-free, lactose-free, kosher)
• Decompensated liver disease
• Congenital or documented acquired QT prolongation
• Electrolyte disturbances, particularly uncorrected hypokalaemia
• Clinically relevant bradycardia
• Clinically relevant heart failure with reduced left-ventricular ejection fraction
• Previous history of symptomatic arrhythmias
• History of clinically significant gastro-intestinal, renal, hepatic, bronchopulmonary, neurological, psychiatric, cardiovascular, endocrinological, , hematological, or allergic disease, metabolic disorder, cancer, or cirrhosis