1. Alterations in the levels of intracellular calcium ([Ca2+]i) and D-myo-inositol-1,4,5-trisphosphate (InsP3) were measured in the murine neuroblastoma cell line clone, N1E-115, by use of the calcium-sensitive dye, fura-2 and a radioreceptor assay, respectively. 2. Exposure of the cells to ATP (100 microM) elicited rapid and transient increases in [Ca2+]i and InsP3, with both responses reaching a maximum between 10-20 s after agonist addition. 3. Investigation of concentration-response data by use of various analogues of ATP suggests the presence of an extracellular receptor which fails to fit into the current classification of purinoceptors. 4. Cross-desensitization experiments suggest that the same receptor can also be activated by the structurally different pyrimidine base, UTP. 5. Application of the tumour-promoting agent, beta-phorbol-12,13 dibutyrate (PDBu) caused a reduction in the increases in both [Ca2+]i and InsP3, suggesting a role for protein kinase C in feedback inhibition of purinoceptor responses in this cell line. 6. In summary, we present the first evidence for the existence of an atypical purinoceptor on a cell line of CNS origin. This receptor is linked to stimulation of phosphoinositide turnover and subsequent mobilisation of intracellular calcium.