Transcription factors GATA-4 and GATA-6 are expressed during normal adrenocortical development in mice and humans, and in vitro studies have linked them to adrenal steroidogenesis. GATA-4 is highly expressed in the adrenocortical tumors of gonadectomized mice, whereas GATA-6 is down-regulated in the tumor area. Based on these findings we studied GATA-4 and GATA-6 expression in 39 human adrenocortical tumors using RT-PCR, Northern analysis and immunohistochemistry. 6/18 adenomas and 4/11 carcinomas were positive for GATA-4 mRNA. GATA-6 mRNA was expressed in 19/19 adenomas and 9/10 carcinomas, and GATA-6 immunoreactivity was remarkably lower in adrenocortical carcinomas than in adenomas (p < 0.05). Some of the steroidogenically active human adrenocortical cells (NCI-H295R) were weakly positive for GATA-4, whereas steroidogenically inactive cells (ACT-1) were totally GATA-4 negative. In contrast, both cell lines expressed GATA-6. GATA expression patterns similar to the animal models can thus be observed in human adrenocortical tumors, but the pathophysiological significance of these findings remains to be elucidated.