DISEASE CHARACTERISTICS: Histologically or cytologically confirmed metastatic malignant melanoma At least 1 measurable lesion At least 2.0 cm in longest dimension No truly non-measurable lesions including the following: Bone lesions Leptomeningeal disease Ascites Pleural/pericardial effusion Inflammatory breast disease Lymphangitis cutis/pulmonis Abdominal masses not confirmed and followed by imaging techniques Cystic lesions No known brain metastases requiring active treatment

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-1 Life expectancy: At least 3 months Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 2.5 times upper limit of normal (ULN) AST no greater than 2.5 times ULN Renal: Creatinine no greater than 1.5 times ULN OR Creatinine clearance greater than 60 mL/min Cardiovascular: No symptomatic congestive heart failure No unstable angina pectoris or cardiac arrhythmia Other: No known allergy to compound of similar chemical or biologic composition to PS-341 No other uncontrolled concurrent illness No ongoing or active infection No psychiatric illness that would preclude study Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: More than 4 weeks since prior immunotherapy or biologic therapy and recovered No concurrent immunotherapy Chemotherapy: No prior chemotherapy No concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: More than 4 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: No other concurrent investigational therapy No concurrent combination antiretroviral therapy for HIV-positive patients No other concurrent investigational or commercial agents for treatment of melanoma