Between 1987 and 1990 21 patients with proven adenocarcinoma of the pancreas were treated with chemotherapy in four different phase II studies. For 14 patients, serial measurements of CA19-9 serum levels and clinical evaluations of response by computed tomography scan and/or ultrasound were available. Clinical stable disease and progressive disease were accompanied by stable or exponentially rising serum levels of CA19-9. One patient with clinical partial remission showed a 90% decline of CA19-9. However, a 75% decline of CA19-9 was also observed in a patient with rapidly progressive disease. These data seem to indicate that the CA19-9 serum level may be used as an easy and sensitive tool to evaluate progressive disease during chemotherapy.