Adenosine triphosphate (ATP) is one of the cotransmitters that are commonly released at catecholaminergic and cholinergic nerve terminals. The glial cell type most closely associated with the synapse is the astrocyte and, thus, is the next cellular element beside the postsynaptic neuron to face the transmitters released. This report gives evidence of P2-purinoceptors on cultured astroglial cells. Upon stimulation with nucleoside triphosphates and nucleoside diphosphates, the cells respond with synthesis of prostaglandins of the D2 type, which is the predominant prostaglandin made in rat brain. Nucleoside triphosphate analogues, such as 5'-adenyl-imido diphosphate, beta,gamma-methylene, or alpha,beta-methylene ATP were less effective than ATP or its non-hydrolysable analogue ATP [gamma S]. The receptor was desensitized by ATP [gamma S] within 15 min, whereas desensitization by alpha,beta-methylene ATP was significantly delayed. 8-phenyl-theophylline (10(-4) M) had no influence on ATP-stimulated prostaglandin synthesis. Adenosine 5'-monophosphate (AMP) and adenosine were unable to stimulate prostaglandin D2 formation. According to the common nomenclature for purinoceptors, the described astroglial receptor would fulfill the characteristics of a P2-purinoceptor. Furthermore, it is shown that pertussis toxin sensitive G-proteins influence some early step in prostaglandin synthesis. The inactivation of these proteins results in reduced prostaglandin formation. It is assumed that ATP serves as an important mediator in the cross-talk between neurons and astroglial cells at the synaptic cleft.