Summary ― The changes in levels of prolactin (PRL) and growth hormone (GH) in plasma and the pituitary gland and their transcripts were measured in turkey hens at different physiological stages by radioimmunoassay and dot blot hybridization analysis, respectively. The levels of tPRL mRNA in the pituitary gland increased from those of the immature group to the egglaying group, reaching a maximum during the incubation and a minimum during the moulting stages. Changes in pituitary levels of PRL and PRL mRNA followed a similar trend and consequently were highly correlated (r 2 = 0.83), whereas a significant but lower correlation was observed between circulating and pituitary levels (r 2 = 0.62). Less significant changes were measured for tGH mRNA, with maximum and minimum levels measured in the pituitaries of egglaying and non-laying hens, respectively. These data suggest that although changes in con