Inclusion Criteria

1. Age 18 years or above
2. Adequate hematologic, hepatic, and renal function
3. Histologically confirmed, new diagnosis of PTCL
4. Eligible for CHOP regimen
5. Measurable disease based on Cheson 2007 criteria
6. Eastern Cooperative Oncology Group (ECOG) performance status < 2
7. Willing to perform at least two methods of contraception
8. Negative pregnancy test of females with childbearing potential. 

Exclusion Criteria

1. Active concurrent malignancy (except non melanoma skin cancer or carcinoma in situ of the cervix) or life threatening disease. If there is a history of prior malignancies or life threatening diseases, the patient must be disease free for at least 5 years.
2. Congestive heart failure Class III/IV according to the New York Heart Association (NYHA) Functional Classification.
3. Uncontrolled hypertension
4. Central nervous system (CNS) metastases .
5. Active uncontrolled infection, underlying medical condition, or other serious illness that would impair the ability of the patient to receive protocol treatment
6. Major surgery within 30 days prior to enrollment.
7. Use of any investigational drugs, biologics, or devices within 30 days prior or during the study treatment.
8. Previous exposure to pralatrexate.
9. Pregnant or breastfeeding.