The nuclear DNA contents of tumor cells in 73 patients with endocrine gastrointestinal tumors, 19 patients with endocrine pancreatic tumors (EPT) and 54 patients with malignant carcinoid tumors were determined before and after treatment. The DNA profiles were divided into diploid and aneuploid. In untreated patients, 9 out of 10 (90%) primary EPT and all 9 primary malignant carcinoid tumors (100%) were diploid. Tumor cell imprints from liver metastases of patients with untreated EPT showed aneuploidy in 5 of 11 cases, but only in 7 out of 46 DNA records from patients with untreated carcinoid liver metastases. DNA alteration from diploid to aneuploid profiles occurred in 2 patients with endocrine pancreatic tumors who had received chemotherapy. A change from diploid to aneuploid records was also seen in 7/23 (30%) carcinoid tumors after treatment. The DNA patterns before and after treatment did not show any correlation with survival or treatment response.