Primary cultures of dispersed hypothalamic cells were prepared from 18- to 19-day-old rat fetuses. Morphological studies revealed two types of cells having typical glial and neuronal appearances. Immunostaining of cells in culture was positive for neurophysin. The incubation medium contained radioimmunoassayable luteinizing hormone-releasing hormone, vasopressin, β-endorphin and adrenocorticotropin hormone. The present data suggest that hypothalamic cells in primary culture secrete immunoreactive hormones or peptides; however, they do not seem to store significant amounts of these peptides.