On the basis of our previous finding that prolactin (PRL) cells of the bullfrog (Rana catesbeiana) contain immunoreactive alpha-subunit of pituitary glycoprotein hormones, experiments were conducted to see whether the immunoreactive alpha-subunit is released from PRL cells. Cell immunoblot analysis revealed that approximately 10% of cells that released immunoreactive PRL also released immunoreactive alpha-subunit. Western blot analysis of the culture media revealed that a considerable amount of the free form of alpha-subunit was released from the dispersed anterior pituitary cells. Moreover, it was found that addition of alpha-subunit to the culture medium enhanced PRL release. The results raise the possibility that alpha-subunit secreted by PRL cells acts as an autocrine and/or paracrine factor.