BACKGROUND Recent investigations indicate that in 50% of patients with gastric cancer, beta-hCG-positive cells can be found in the tumour by immunohistochemical investigations. The objective of this study was to investigate how often beta-hCG-immunoreactive gastric carcinomas were accompanied by an elevation in serum beta-hCG, that could have been used as a course control variable. METHODS In 54 patients with gastric carcinoma a monoclonal antibody directed against beta-hCG was used for immunohistochemical marking in the APAAP system. The evaluation was graded positive or negative. In parallel, serum beta-hCG was determined preoperatively using an enzyme immunoassay (MEIA). Tumour stage, grading and tumour localization were determinants in the evaluation. RESULTS We found that 41% (22 of 54) of the carcinomas induced a positive immunohistochemical response to beta-hCG, regardless of their location in the stomach. In relation to tumour stage, a positive beta-hCG immunoreactivity was apparent in 27% (6/22) of tumours without lymph node or distant metastases (T1-4N0M0), in 54% (7/13) of tumours with lymph node and without distant metastases (T1-4N > or = 1M0) and in 47% (9/35) of tumours with distant metastases. Poorly differentiated tumours (G3-4) were positive in 42% (15/36) and well-differentiated tumors (G1-2) in 39% (7/18) of cases. In only 1 patient was the beta-hCG level in serum elevated, however. CONCLUSIONS beta-hCG-Positive gastric carcinomas are found more frequently in advanced tumour stages and poorly differentiated carcinomas. These carcinomas, however, seem not to excrete beta-hCG in sufficient amounts to produce measurable serum values. Therefore, beta-hCG cannot be used a prognostic factor or for course control. The relevance of beta-hCG expression of tumour cells to the patients' prognosis remains obscure.