DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed solid tumor

  • Advanced, metastatic, or recurrent disease
  • No curative therapy exists
• Measurable or evaluable disease

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• WHO 0-2

Life expectancy:

• At least 3 months

Hematopoietic:

• Absolute granulocyte count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• Hemoglobin at least 9 g/dL

Hepatic:

• Bilirubin no greater than 1.5 mg/dL (unless due to Gilbert's syndrome)
• SGOT OR SGPT no greater than 2 times upper limit of normal (ULN) (5 times ULN if liver metastases present)

Renal:

• Creatinine no greater than 1.5 mg/dL
• Creatinine clearance at least 60 mL/min

Other:

• No unstable or severe concurrent medical condition that would preclude study participation
• No sociological or familial condition that would preclude study compliance
• No psychological or addictive disorder that would preclude study compliance
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• At least 4 weeks since prior chemotherapy (6 weeks for nitrosourea or mitomycin) and recovered

Endocrine therapy:

• Not specified

Radiotherapy:

• At least 4 weeks since prior radiotherapy and recovered
• No prior radiotherapy to more than 40% of bone marrow

Surgery:

• Not specified

Other:

• At least 2 weeks since prior blood transfusions
• At least 4 weeks since prior investigational agent and recovered
• No prior glycinamide ribonucleotide formyltransferase (GARFT) inhibitor
• No concurrent extradietary folate supplements
• No concurrent allopurinol
• No other concurrent anticancer or investigational agents