A total of 123 manifestations (97 primary tumours and 26 metastases) of neuroendocrine tumours of the gastrointestinal tract observed in 95 patients was investigated for the prognostic value of clinical, histological and DNA cytophotometric parameters. Metastases almost exclusively occurred among ileal carcinoids, which also were responsible for all 14 cases of lethal outcome observed during the follow-up period of mean 42 months. Aneuploid DNA values could be determined significantly more frequently among ileal than in non-ileal carcinoids and showed - upon analysis of the total group of gastrointestinal neuroendocrine tumours - a significant correlation to lethal course of disease. In addition, among 18 cases with primary and secondary carcinoid manifestations available for DNA cytophotometry, an association between the DNA content of metastatic neuroendocrine tumours and prognosis came to light. When applied to the group of ileal neoplasms, however, the parameter DNA content did not allow a better prognostic assessment.