This study is being done to see if an experimental drug called recombinant interleukin-21 (rIL-21) when given to patients with stage 4 malignant melanoma or stage 4 kidney cancer is safe and has any effect on these types of cancers.

This is a phase 1 safety study. Everyone enrolled and eligible will be given rIL-21. The study has 2 parts, Part A will determine how high a dose of rIl-21 can be safely given to patients with these types of cancers. Part B will determine if the drug is of any benefit to patients with these types of cancers. Part A may have up to 7 different dose groups. Beginning with the lowest dose, 3 patients will be treated and will be watched for side effects. If the side effects are not severe, the next group of 3 patients will recieve a higher dose. This cycle is repeated until the highest tolerated dose group is found.

Inclusion Criteria:

• 18 years and older with stage 4 metastatic malignant melanoma or stage 4 metastatic kidney cancer
• ECOG status of 0 or 1
• Patients must have adequate liver, kidney and bone marrow function

Exclusion Criteria:

• Known ocular melanoma
• Suspected or confirmed brain metastases
• Patient cannot have had a bone marrow transplant