Pectic acid extracted from plants increases the secretion of prolactin (PRL) when injected intravenously into ewes or fed to rats. Fragments of ewe hypophysis and lactating rabbit mammary gland incubated in vitro in the presence of pectic acid secreted more PRL and caseins compared to the controls. However, it is not known whether pectic acid directly stimulates PRL secretion in pituitary or interference of factors from hypophysis is required for this process. GH3/B6 cells, a clonal strain of rat pituitary, were cultured and incubated with pectic acid (2.5-100 microg/mL). The integrity of cells was examined under pectic acid treatment microscopically. Controls or pectic acid treated cells were assayed for their ability to produce PRL. The PRL was assayed by Western-blotting and Radioimmunoassay. pectic acid did not have any significant effect on the viability of cells. After being incubated with pectic acid, the cells started to become circular and protuberant shape. The maximum stimulation and PRL secretion occurred at 100 microg/mL concentration within 30 min of incubation with pectic acid. pectic acid could stimulate the release of PRL in GH3/B6 cells in the short-term incubation. This result suggested that pectic acid is a non-toxic agent that could directly stimulate PRL secretion in pituitary cells without any interference of hypophysis.