Inclusion Criteria:

- Patient has one of the following peripheral T-cell lymphoma (PTCL) subtypes confirmed
by an independent central pathology reviewer, using the Revised European American
Lymphoma World Health Organization disease classification:

- T/natural killer (NK)-cell leukemia/lymphoma

- Adult T-cell lymphoma (TCL)/leukemia (human T-cell leukemia virus 1+)

- Angioimmunoblastic TCL

- Anaplastic large cell lymphoma (ALCL), primary systemic type, excluding
anaplastic lymphoma kinase positive (ALK+) with International Prognostic Index
(IPI) score less than 2 at initial diagnosis and complete response (CR) after
CHOP-based therapy

- PTCL-unspecified

- Enteropathy-type intestinal lymphoma

- Hepatosplenic TCL

- Subcutaneous panniculitis TCL

- Transformed mycosis fungoides (tMF)

- Extranodal T/NK-cell lymphoma nasal or nasal type

- Primary cutaneous gamma-delta TCL

- Primary cutaneous CD8+ aggressive epidermic cytotoxic TCL

- Documented completion of at least 6 cycles of CHOP-based therapy:

- CHOP 21

- CHOP 14

- CHOP + etoposide

- Other CHOP variants: substitution allowed for 1 component with a drug of the
same mechanism of action. Additional components, except alemtuzumab, are
allowed. Rituximab may be added if not given within 3 cycles of randomization.

- Patient has achieved CR or partial response (PR) per per investigator's assessment
following completion of CHOP-based therapy and has had radiological assessment within
21 days prior to randomization.

- Eastern Cooperative Oncology Group performance status less than or equal to 2.

- Adequate blood, liver, and kidney function as defined by laboratory tests.

- Women of childbearing potential must have a negative serum pregnancy test within 14
days prior to randomization and agree to practice a medically acceptable
contraceptive regimen from study treatment initiation until at least 30 days after
the last administration of pralatrexate.

- Men who are sexually active, including those with a pregnant partner, must agree to
practice a medically acceptable barrier method contraceptive regimen (eg, condoms)
while receiving pralatrexate and for 90 days after the last administration of
pralatrexate.

- Has given written informed consent.

Exclusion Criteria:

- Patient has:

- Precursor T/NK neoplasms

- ALCL (ALK+) with IPI score less than 2 at initial diagnosis and CR after
CHOP-based therapy

- T cell prolymphocytic leukemia

- T cell large granular lymphocytic leukemia

- Mycosis fungoides, except tMF

- Sézary syndrome

- Primary cutaneous CD30+ disorders: ALCL and lymphomatoid papulosis

- If there is a history of prior malignancies other than those below, must be disease
free for at least 5 years. Patients with malignancies listed below less than 5 years
before study entry may be enrolled if they have received treatment resulting in
complete resolution of the cancer and have no clinical, radiologic, or laboratory
evidence of active/recurrent disease.

- non-melanoma skin cancer

- carcinoma in situ of the cervix

- localized prostate cancer

- localized thyroid cancer

- Receipt of prior chemotherapy (CT) or radiation therapy (RT) for PTCL, other than a
single allowed CHOP regimen, except:

- Patients with nasal NK lymphoma who received local RT less than 4 weeks prior to
randomization.

- Patients with tMF who received 1 systemic single-agent CT (except methotrexate)
prior to transformation.

- Prior exposure to pralatrexate.

- Receipt of systemic corticosteroids within 3 weeks of study treatment, unless patient
has been taking a continuous dose of 10 mg/day or less of oral prednisone or
equivalent for at least 4 weeks or as part of a CHOP prednisone taper.

- Planned use of any treatment for PTCL during the course of the study.

- Patient has:

- Human immunodeficiency virus (HIV)-positive diagnosis with a CD4 count of less
than 100 mm3 or detectable viral load within past 3 months and receiving
anti-retroviral therapy.

- Hepatitis B (HBV)-positive serology and is receiving interferon therapy or has
liver function test results outside the parameters of study inclusion criteria.
Other antiviral therapies are permitted if at a stable dose for at least 4
weeks.

- Hepatitis C (HCV) virus with detectable viral load or immunological evidence of
chronic active disease or receiving/requiring antiviral therapy.

- Symptomatic central nervous system metastases or lesions requiring treatment.

- Uncontrolled hypertension or congestive heart failure Class III/IV per the New
York Heart Association's Heart Failure Guidelines

- Active uncontrolled infection, underlying medical condition including unstable
cardiac disease, or other serious illness impairing the ability of the patient
to receive protocol treatment.

- Major surgery within 2 weeks prior to study entry, except for line placement or
biopsy procedure.