The safety and efficacy of a once-daily regimen that combines emtricitabine, didanosine, and efavirenz was studied among 40 previously untreated human immunodeficiency virus (HIV)-infected patients. The median plasma HIV RNA level was 4.77 log(10) copies/mL at baseline and decreased by a median of 3.5 log(10) copies/mL at 24 weeks, with 98% and 93% of patients achieving plasma HIV RNA levels <400 and <50 copies/mL, respectively. The median CD4 cell count was 373 cells/microL at baseline and increased by a median of 159 cells/microL at week 24. The most common treatment-related adverse events were mild to moderate central nervous system symptoms (73% of patients), diarrhea (33%), rashes (10%), and biochemical abnormalities. Adverse reactions led to permanent drug discontinuation in only 1 patient. The once-daily combination therapy of emtricitabine, didanosine, and efavirenz was safe and demonstrated strong antiviral and immunologic effects that lasted for the 24-week period of the study.