• This study will evaluate the safety and pharmacokinetics of pemetrexed in patients with third-space fluid. This outcome will be fully evaluated once the last patient receiving study treatment has discontinued from study treatment.
• Secondary: This study will identify increases in the toxicity of pemetrexed, assess the clinical relevance of any alterations in pemetrexed pharmacokinetics and provide pemetrexed dosing recommendations, in patients with third-space fluid.

• Adverse events [ Time Frame: every cycle ] [ Designated as safety issue: Yes ]
• Pharmacokinetics [ Time Frame: cycle 1, cycle 2 ] [ Designated as safety issue: Yes ]
• Pemetrexed dosing recommendations [ Time Frame: every cycle ] [ Designated as safety issue: Yes ]

This study will test the effects of pemetrexed on mesothelioma and lung cancer patients with fluid around their lungs or abdomen.

• Non-Small Cell Lung Cancer
• Mesothelioma
• Lung Neoplasms

Inclusion Criteria:

• Diagnosis of locally advanced or metastatic (Stage III or IV at entry) non-small cell lung cancer or mesothelioma
• Presence of third-space fluid (fluid around the lungs or abdomen).
• Measurable lesions are not required for enrollment in this study.
• Prior anticancer treatment (except radiation) must be completed at least 3 weeks prior to study enrollment, and the patient must have recovered from the sharp toxic effects the anticancer treatment.
• Estimated life expectancy of at least 8 weeks.

Exclusion Criteria:

• Have received treatment within the last 30 days with a drug that was not a marketed product
• Active infection that, in the opinion of the investigator, would not allow the patient to tolerate therapy.
• Pregnancy.
• Breast-feeding.
• Significant weight loss (that is, greater than or equal to 10% of body weight) over the 6 weeks before study entry.