Inclusion Criteria:

- Clinical diagnosis of B-cell Non-Hodgkin's Lymphoma, using the Revised European
American Lymphoma (REAL) World Health Organization (WHO) disease classification

- Measurable disease

- Progressive or persistent disease after ≥ 1 prior treatment(s)

- Recovered from toxic effects of prior treatment

- At least 4 weeks since most recent cytotoxic therapy

- Easter Cooperative Oncology Group (ECOG) performance status ≤ 2

- Adequate blood, liver, and kidney functions as defined by laboratory levels

- 1.0 mg/day orally of folic acid for at least 7 days prior & 1 mg intramuscular of
vitamin B12 within 10 weeks of the planned start of pralatrexate

- Females of childbearing potential must agree to use medically acceptable birth
control from start of pralatrexate until at least 30 days after the last
administration of pralatrexate and must have a negative serum pregnancy test within
14 days prior to the first day of study treatment

- Males who are not surgically sterile must agree to use medically acceptable birth
control from start of pralatrexate until at least 90 days after the last
administration of pralatrexate

- Available for repeat dosing and follow-up

- Able to give written informed consent

Exclusion Criteria:

- Relapsed patients with diffuse large B-cell lymphoma (DLBCL) who are candidates for
high-dose therapy and autologous stem cell transplantation (SCT) and for whom
high-dose therapy and autologous SCT is a standard curative option

- Active concurrent malignancy (except non-melanoma skin cancer or carcinoma in situ of
the cervix). If there is a history of prior malignancies other than those exceptions
listed above, the patient must be disease-free for ≥ 5 years. Patients with other
prior malignancies < 5 years before study entry may still be enrolled if they have
received treatment resulting in complete resolution of the cancer and currently have
no clinical, radiologic, or laboratory evidence of active or recurrent disease

- Congestive heart failure Class III/IV according to the New York Heart Association
Functional Classification

- Uncontrolled hypertension

- Known human immunodeficiency virus (HIV)-positive diagnosis

- Symptomatic central nervous system (CNS) metastases or lesions for which treatment is
required. Patients who received prophylactic CNS treatment are eligible.

- Patients who have undergone an allogeneic SCT

- Patients who have relapsed < 100 days from the time of an autologous SCT

- Patients with disease refractory to peripheral blood SCT or who have relapsed < 100
days from the time of transplant

- Active uncontrolled infection, underlying medical condition, or other serious illness
that would impair the ability of the patient to receive protocol treatment.

- Major surgery within 14 days of enrollment

- Receipt of any conventional chemotherapy or radiation therapy (encompassing a
substantial [> 10%] amount of bone marrow) within 4 weeks (6 weeks for nitrosoureas
or mitomycin C) prior to study treatment or planned use during the course of the
study

- Receipt of systemic corticosteroids within 1 week of study treatment, unless patient
has been taking a continuous dose of no more than 10 mg/day of prednisone or its
equivalent for at least 1 month

- Use of any investigational drugs, biologics, or devices within 4 weeks prior to study
treatment or planned use during the course of the study

- Previous exposure to pralatrexate

- Females who are pregnant or breastfeeding