 ADI-PEG 20 appears to be an effective anti-cancer treatment for human HCC. Pharmacokinetic and pharmacodynamic data indicates a once a week injection of 160 IUm2 of ADI-PEG 20 eliminates all detectable arginine from the circulation for at least 7 days. This treatment appears to be well tolerated. The purpose of this study is to determine the efficacy of this treatment in patients with HCC. Efficacy is a primary end point of this study. No patients will recieve placebo. 