We localized types I, III, IV and VI collagen in the rat anterior pituitary using immunofluorescence staining and identified collagen synthesizing cells using double immunostaining of primary cultured anterior pituitary cells. Collagen types I, III and VI were located around the basement membrane and type IV was found at the basement membrane of the anterior pituitary gland. However, none of these extracellular matrices were observed in glandular cells. Primary cultured cells formed small clusters, although several individual cells remained isolated. Type I collagen was identified at the cytoplasm. Type III collagen appeared at the cytoplasm or along cell profiles as short lines or dots. Types IV and VI collagen appeared as continuous or dotted lines along cell profiles. Double immunostaining revealed that type I collagen was synthesized by GH, PRL, LH, TSH, ACTH and folliculo−stellate cells and that type III collagen was synthesized by PRL, LH, TSH and folliculo−stellate cells. These results show that anterior pituitary cells can synthesize some collagens, and suggest that the types I, III, IV and VI collagen in the anterior pituitary gland may be synthesized by glandular cells in vivo.