functional integrity of anterior pituitary cells separated by a density gradient using a continuous percoll density gradient endocrine cells of the anterior pituitary were separated the cells were obtained from adult female spraguedawley rats which had been ovariectomized for 7 days the gradient revealed two equally sized populations of cells with densities of about 102 and 109 gml ninetytwo per cent of the cellular gh content 64 of lh and 60 of tsh were found in the high density peak sixtyone per cent of the cellular prl appeared in the low density peak immunocytochemical staining of the lh containing cells showed that 74 of the gonadotrophs were in the high density peak after separation the cells retained their responsiveness to lrh trh and grf culture conditions influenced stimulated hormone release before stimulation the cells were cultured either in tissue culture flasks attached cells or in petri dishes cells in suspension for 3 days after trhstimulation suspended thyrotrophs released more tsh than attached thyrotrophs comparing the cells of both peaks attached thyrotrophs of the high density peak showed higher stimulated tshrelease than those of the low density peak the response of the gonadotrophs and somatotrophs to stimulation did not differ when culture conditions were changed the present results demonstrate that the secretory activity of endocrine cells is influenced by culture conditions and should be evaluated fore each cell type