DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed malignancy refractory to existing chemotherapy or for which no standard therapy exists
• Evaluable disease

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• SWOG 0-2

Life expectancy:

• Greater than 3 months

Hematopoietic:

• Absolute neutrophil count greater than 1,500/mm3
• Platelet count greater than 100,000/mm3
• Hemoglobin greater than 8.0 mg/dL

Hepatic:

• Bilirubin less than 2.0 mg/dL
• AST less than 3.0 times upper limit of normal

Renal:

• Creatinine no greater than 2.0 mg/dL

Other:

• No active infection requiring antibiotics
• Not pregnant or nursing
• Fertile patients must use effective barrier contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• At least 3 weeks since prior systemic cytotoxic chemotherapy (including fluorouracil) and recovered
• No prior gemcitabine

Endocrine therapy:

• Prior hormonal therapy allowed
• No concurrent hormonal contraception

Radiotherapy:

• At least 3 weeks since prior radiotherapy to large areas of active bone marrow and recovered

Surgery:

• Prior major surgery allowed and recovered

Other:

• No prior or concurrent antiviral nucleosides