The objectives of this study are to determine the safety and activity profile of multiple doses of MDX-010, and to determine the whether the addition of cytotoxic chemotherapy (decarbazine [DTIC]) can augment the effects of MDX-010 in patients with chemotherapy naïve metastatic melanoma with a tolerable toxicity profile.

Inclusion Criteria

• Clinical diagnosis of unresectable metastatic melanoma.
• No prior chemotherapy for melanoma, and no chemotherapy for other malignancies within 5 years and at least 4 weeks since treatment (surgery, radiation, or immunotherapy) for melanoma.

Exclusion Criteria

Patients who exhibit any of the following conditions at screening will not be eligible for admission into the study:

• Any other prior malignancy, except for the following: adequately treated basal or squamous cell skin cancer or superficial bladder cancer, or any other cancer from which the patient has been disease-free for >=5 years.
• Active autoimmune disease.
• Active infection requiring therapy, or chronic active HBV or HCV, or confirmed reactivity with HIV tests.