A cell line (LCC-18) from a neuroendocrine colonic tumour was established. The tumour cells retained their endocrine characteristics through more than 100 passages and showed positive immunocytochemistry for synaptophysin, vasoactive intestinal polypeptide (VIP) and glucagon. The culture medium also contained VIP and glucagon, which indicates that mechanisms for release of some of the active peptides were preserved. Transplantation of LCC-18 tumour cells into nude rats resulted in tumour formation with similar endocrine characteristics. The c-myc gene was amplified which might have been a prerequisite for establishment of the cell line. The chromosomes in LCC-18 were studied by G-banding and C-banding. The cell line had a distinctive mode in the hypotriploid region, at S = 61. The double minute (Dms) positive stemline karyotype showed numerical and structural aberrations more similar to findings in ordinary colonic adenocarcinomas than to observations in previously studied, pure intestinal neuroendocrine tumours. The Dms may be correlated with amplification of c-myc. LCC-18 may become valuable for studies of neuroendocrine differentiation, regulation of growth and production and release of hormones and for studies of drug effect.