 This is a Phase 1, open-label, single-dose study in approximately 35 subjects with PKU who are 16 to 50 years old. Seven cohorts are planned, each consisting of 5 subjects; the cohorts as planned are 0.001, 0.003, 0.01, 0.03, 0.1, 0.3, and 1.0 mgkg. Increasing doses of rAvPAL-PEG will be assessed sequentially until the final dose is evaluated or any of the stopping criteria are reached. Subjects will each receive a single dose and then will be followed for a total of 42 days 6 weeks with visits to the clinical research unit CRU as specified in the Schedule of Events Toxicity will be measured according to the National Cancer Institute NCI Common Terminology Criteria for Adverse Events CTCAE, v 3. 