We evaluated the safety and efficacy of indinavir 400 mg and ritonavir 400 mg twice daily (RIT/IND 400/400) in HIV-1-infected individuals, using an open label, proof of concept study. All patients received indinavir 400 mg and ritonavir 400 mg twice daily. Patients were followed up to 48 weeks. Nineteen subjects were enrolled, 11 (58%) men and eight (42%) women. The majority were American Black (nine; 47%) or Haitian (eight; 42%). The median baseline plasma HIV-1 viral load (VL) was 5.13 log10 copies/mL and the median CD4 cell count was 112 cells/mm(3). The proportion of compliant patients with VL <400 copies/mL at week 24 was 60% compared with 0% for non-compliant patients (P=0.011 [intent-to-treat] or P=0.085 [on-treatment]). VL at week 4 predicted week 24 VL response. Compliant patients had a median average CD4 cell count increase of 83.2 cells/mm(3) compared with 42.0 cells/mm(3) for non-compliant patients (P=0.010). The median average changes in triglycerides and cholesterol were significantly higher in compliant patients. This is a potent, safe combination for the treatment of HIV-1. VL at week 4 is predictive of viral outcome at week 24. Fasting serum cholesterol and triglycerides were significantly elevated during the study.