A 48-Week, Randomised, Study to Describe the Pharmacokinetic Profile and Durability of Atazanavir-Saquinavir-Ritonavir Once Daily and Describe the Pharmacokinetic Profile of Saquinavir-Ritonavir Using Saquinavir 500mg Formulation: the ASK-500 Study (ASK-500)

Inclusion Criteria: HIV-1 infected individuals aged 18 years or over On stable antiretroviral therapy for at least three months consisting of nucleoside reverse transcriptase inhibitors and protease inhibitors OR On stable antiretroviral therapy for at least three months consisting of atazanavir-saquinavir-ritonavir Undetectable HIV RNA viral load for past three months Exclusion Criteria: Individuals receiving on non-nucleoside reverse transcriptase inhibitors within the past three months Individuals currently receiving other enzyme inducing agents (as per Individuals receiving ritonavir at doses greater than 100 mg bid Active AIDS defining illnesses Previously documented intolerance or virological failure to saquinavir Previously documented intolerance or virological failure to atazanavir Patients who are co-infected with Hepatitis B and are likely to require, in their clinician's opinion, HBV nucleoside therapy during the study. Female patients who are pregnant, breastfeeding, or who plan to become pregnant during the study Any current clinical or laboratory parameter of ACTG Grade 4 (except lipids & CK) Evidence of ongoing alcohol and/or drug or substance abuse that would result in the patient being unreliable in fulfilling the conditions of this protocol Prior non-adherence to antiretroviral treatment regimens that would result in the patient being unreliable in fulfilling the conditions of this protocol Evidence of active opportunistic infection, intercurrent illness, drug toxicity or any other condition that would preclude the patient from taking the prescribed antiretroviral regimen Conditions that might interfere with evaluation of the disease under study. Conditions/allergies that may compromise the safety of the patient.