Hypothalamic cell cultures represent a suitable model for studying the role of hormones during the development of the hypothalamus. In vitro studies have shown that oestradiol increases the neurite length in some hypothalamic nuclei and the number of LH-RH neurons. Triiodothyronine had no effect on the number of neurons but controlled the size and the neurite length of hypothalamic dopaminergic neurons. In contrast, mesencephalic DA neurons are regulated differently by T3. The effects of hormones in culture are correlated with the presence of specific nuclear binding sites. At last, serum-free cultures have demonstrated the importance of the interaction between hormones (T3, corticosterone) and others diffusible factors (polyunsaturated fatty acids) on the potassium evoked release of thyroliberin and on the maturation of synapses.