Inclusion Criteria:

• Diagnosis of PKU with both of the following:
• Current blood Phe concentration of ≥600 µmol/L at Screening.
• Average blood Phe concentration of ≥600 µmol/L over the past 3 years, using available data.
• Willing and able to provide written, signed informed consent, or, in the case of participants under the age of 18, provide written assent (if required) and written informed consent by a parent or legal guardian, after the nature of the study has been explained, and prior to any research-related procedures.
• Willing and able to comply with all study procedures.
• Between the ages of 16 and 50 years, inclusive.
• Females of childbearing potential must have a negative pregnancy test at Screening and be willing to have additional pregnancy tests during the study. Females considered not of childbearing potential include those who have been in menopause at least 2 years, or had tubal ligation at least 1 year prior to Screening, or who have had total hysterectomy.
• Sexually active subjects must be willing to use an acceptable method of contraception while participating in the study.
• Stable diet with no significant modifications during the 4 weeks preceding the administration of study drug.
• In generally good health as evidenced by physical examination, clinical laboratory evaluations (hematology, chemistry, and urinalysis), and electrocardiogram (ECG) at Screening.

Exclusion Criteria:

• Use of any investigational product or investigational medical device within 30 days prior to Screening, or requirement for any investigational agent prior to completion of all scheduled study assessments.
• Pregnant or breastfeeding at Screening or planning to become pregnant (self or partner) or to breastfeed at any time during the study.
• Concurrent disease or condition that would interfere with study participation or safety (eg, history or presence of clinically significant cardiovascular, pulmonary, hepatic, renal, hematologic, gastrointestinal, endocrine, immunologic, dermatologic, neurological, oncologic, or psychiatric disease).
• Any condition that, in the view of the Principal Investigator (PI), places the subject at high risk of poor treatment compliance or of not completing the study.
• Known hypersensitivity to rAvPAL PEG or its excipients.
• Alanine aminotransferase (ALT) concentration > 2 times the upper limit of normal.
• Creatinine above the upper limit of normal.
• Donation of blood or plasma within 30 days prior to the administration of study drug.
• Use of any over-the-counter (OTC) medication, including vitamins, within 7 days prior to the administration of study drug, without evaluation and approval by the Investigator.
• Use of any prescription medication within 14 days prior to the administration of study drug without evaluation and approval by the Investigator.
• Treatment with any drug known to affect hepatic enzyme activity, including (but not limited to) barbiturates, phenothiazines, cimetidine, or carbamazepine, within 30 days prior to study drug administration.
• Use of any tobacco products within 60 days prior to study drug administration.
• Positive urine screen for use of nicotine (cotinine) or drugs of abuse (amphetamines, barbiturates, benzodiazepines, cocaine, cannabinoids, and opiates).
• Positive test or has been treated for hepatitis B, hepatitis C, or human immunodeficiency virus (HIV).