Medullary thyroid carcinoma (hMTC) cells were established from nine patients with MTC disease to initiate a new approach of adjuvant medical therapy in these patients. We measured calcitonin (CT) secretion, DNA synthesis, and cell proliferation in vitro and their response to various substances. Nerve growth factor (NGF) (0.01 to 10 micrograms/ml), glucagon (0.01 to 100 micrograms/ml), and isoproterenol (4 to 500 micrograms/ml) stimulated CT secretion and DNA synthesis in hMTC cells. Other substances, calcium (1.0 to 15 mmol), pentagastrin (1.0 to 50 mumol), dibutyryl-cyclic-adenosine-monophosphate (1.0 to 100 mumol), and phorbol ester TPA (1.0 to 100 nmol), stimulated CT secretion but not DNA synthesis. In addition, NGF enhanced cell proliferation of hMTC cells 2- to 3- fold and caused an increased sensitivity of these cells for chemotherapy in vitro. Thus 0.5 microgram/ml doxorubicin (half-maximal effective dose) induced a cell death rate of up to 32.8%, which was enhanced by preincubation with NGF to 68.1% (1.0 microgram/ml, NGF) and to 100% (10.0 micrograms/ml, NGF), respectively. Pulsative stimulation of APUD cell carcinomas with NGF may therefore improve the response rate of these tumors to chemotherapy, which would be of significant clinical importance for patients with residual postoperative MTC tissue.