Long-time culturing of neuroendocrine tumors from gut and pancreas obtained by surgery was performed with the addition of different growth factors, such as nerve growth factor (NGF), fibroblast growth factor (FGF) and platelet derived growth factor (PDGF) to Hite's medium. Furthermore, the cells were also cultured on epithelial cell matrix (ECM) coated flasks with or without 5% fetal calf serum (FCS) supplemented to the medium. In ECM coated flasks the cells displayed a flattened, non-overlapping pattern and sometimes glandular formation. On the addition of 5% FCS to the culture medium single cells often appeared in cord-like pattern. Culturing in uncoated flasks led to free floating cell colonies or cell clusters attached to fibroblasts present. When different growth factors were added to tumor cells in uncoated culture flasks, no morphological difference could be noticed between the experiments. The tumor cells aggregated to big cell colonies, free-floating in the medium. However, the addition of growth factors to the culture medium showed varying degrees of positive silver staining in cultured tumor cells, while cells cultured in Hite's medium only, with or without FCS supplemented, were negative. The result might indicate that the cells cultured with growth factors retained their endocrine differentiation even after long-term culture. This observation correlated to positive immunostaining to chromogranin A and synaptophysin. Different growth factors might stimulate different fractions of tumor cells to retain the endocrine characteristics.