Inclusion Criteria:

- Histologic or cytologic diagnosis of Small Cell Lung Cancer (SCLC).

- Functional stage from 0 to 2 of the ECOG functional scale

- No previous systemic chemotherapy, immunotherapy or biologic therapy for SCLC.

- Previous bone marrow radiotherapy less than 25% is allowed.

- There must be at least one measurable lesion that complies with the solid tumor
response evaluation criteria.

- Appropriate organic function.

- Life expectancy estimated at 12 weeks minimum.

- Females must be surgically sterile, postmenopausal or follow approved medical
contraceptive methods during the treatment period and 6 months afterwards. Males must
be surgically sterile or use a contraceptive method during the treatment period and
during 6 months after treatment.

- The patient must be compliant and located close to the trial area for appropriate
follow-up.

- The patient or his/her legal representative must sign an informed consent document.

- Patients must be at least 18 years of age.

Exclusion Criteria:

- Having received treatment for the last 30 days with a drug that has not obtained
regulatory approval.

- Having participated in a previous pemetrexed trial.

- Mixed histologic diagnosis of SCLC and NSCLC.

- Concurrent illness.

- Having an active infection.

- Severe cardiac disease.

- Having received recently or concurrently a vaccine against yellow fever.

- Having suffered a previous malignant process other than SCLC.

- Central nervous system (CNS) metastases require concurrent corticoid therapy. Treated
and stable CNS metastases are allowed.

- Clinically relevant fluid accumulation in the third space.

- Significant weight loss (greater than or equal to 10%) within 6 weeks prior to trial
inclusion.

- Concurrent administration of any other anti-tumor treatment.

- Severe renal failure.

- Unable to discontinue administration of non-steroidal anti-inflammatory (NSAIDS)
agents.

- Inability or unwillingness to take folic acid and vitamin B12 supplements.

- Inability to take corticoids.