High levels of maternal estrogens are likely to gain access to the fetal brain, yet little is known regarding the role of the steroid hormone 17beta-estradiol in neuronal differentiation and maturation of primate neurons. Previous research documented the presence of estrogen receptors during development in the hippocampus and cortex of the primate brain, but the functional significance of steroid exposure has not been widely investigated. Using both an in vitro preparation of primary hippocampal and frontal cortex neurons and Western blot analysis of fetal hippocampal and frontal cortex tissue, we documented the effects of in utero and acute in vitro exposure to 17beta-estradiol on the development of neuronal responsiveness to the amino acid transmitters gamma-aminobutyric acid (GABA) and glutamate in fetal baboon, Papio anubis, hippocampal, and cortical neurons. We found that in utero 17beta-estradiol exposure enhanced the excitatory action of the GABAergic system on immature cortical and hippocampal neurons, as manifest by increases in intracellular calcium after transient muscimol application and changes in the relevant ion cotransporters. Acute exposure to 17beta-estradiol in vitro had limited effect on GABAergic responses in cultured hippocampal and frontal cortex neurons. Moreover, there was limited effect of both prolonged in utero and acute estradiol on the response to glutamatergic system activation, consistent with previous findings in the rat. Along with documenting a prominent role for 17beta-estradiol in maturation of the GABAergic system, these findings increase our understanding of neuronal differentiation and maturation in the fetal primate brain.