Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone-(GH), prolactin-(PRL) and thyroid stimulating hormone-beta-(TSH beta) encoding genes. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully used the cell aggregate culture system for chicken pituitary cells to study the effect of TRH administration on the ggPit-1* ( chicken Pit-1), GH and TSH beta mRNA expression in vitro. In pituitary cell aggregates of 11-day-old male broiler chicks the ggPit-1* mRNA expression was significantly increased following TRH administration, indicating that the stimulatory effects of TRH on several pituitary hormones are mediated via its effect on the ggPit-1* gene expression. Therefore, a semi-quantitative RT-PCR method was used to detect possible changes in GH and TSH beta mRNA levels. TRH affected both the GH and TSH beta mRNA levels. The results of this in vitro study reveal that ggPit-1* has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH and TSH beta in the chicken pituitary.