Current standard-of-care antiviral treatment for patients with chronic hepatitis C is combination therapy with pegylated interferon (PEG-IFN) alfa plus ribavirin. Two large clinical trials determined that each PEG-IFN alfa compound, when given in combination with ribavirin, results in overall sustained virological response (SVR) rates of approximately 50%; SVR rates in patients infected with hepatitis C virus (HCV) genotype 1 are typically lower (42-46%). Differences in study design, treatment regimens, and patient populations preclude comparison of the data across trials; therefore, the most effective use of PEG-IFN alfa in combination with ribavirin is unclear. The Individualized Dosing Efficacy vs Flat Dosing to Assess Optimal Pegylated Interferon Therapy (IDEAL) study is a phase 3b, randomized, parallel-group, US multicentre trial in treatment-naive genotype 1 patients with chronic hepatitis C. Initially, this study was undertaken to evaluate the efficacy and safety of weight-based ribavirin dosing (800-1400 mg / day) and PEG-IFN alfa-2b dosing (arm 1: PEG-IFN alfa-2b 1.5 microg / kg / week; arm 2: PEG-IFN alfa-2b 1.0 microg / kg / week). However, because a clinical trial directly comparing the efficacy and safety of PEG-IFN alfa-2a and alfa-2b in combination with weight-based ribavirin dosing has not been performed, an additional arm (arm 3: PEG-IFN alfa-2a 180 microg / week plus ribavirin 1000-1200 mg / day) was included to address this important issue. IDEAL is fully enrolled (>3000 patients) and complete study data, including SVR rates, are expected in early 2008. Herein, we present the scientific rationale and study design, discuss key data from other trials, and summarize our expectations of this study.