Patients receive gemcitabine IV over 30 minutes followed by irinotecan IV over 30 minutes on days 1 and 15. Patients also receive flavopiridol IV over 60 minutes on days 2 and 16. Treatment repeats every 28 days for up to 6 courses in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients receive escalating doses of flavopiridol until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 3 or 2 of 6 patients experience dose-limiting toxicity.