Human astrocytoma cells were studied using whole-cell patch-clamp recording. Voltage-dependent outwardly-rectifying anion currents were identified in primary cultures of six freshly resected human brain tumors and in seven established anaplastic astrocytoma/glioblastoma cell lines (U251MG, CH235MG, U373MG, U105MG, D54MG, SK-MG-1, and STTG1). Anion currents were not observed in normal, non-neoplastic glial cells, nor in human tumor-derived cells of non-glial origin (melanoma, breast cancer, neuroblastoma, rhabdomyosarcoma). Currents activated at potentials >50mV and showed large transients upon termination of voltage steps. Currents reversed at the predicted equilibrium potential for chloride ions and could also be recorded when CI− was replaced by F−, Br− or I−. Currents were inhibited by the CI− channel blockers chlorotoxin, DIDS, and DNDS. These CI− currents may play a role in the growth control of astrocytoma cells. © Rapid Science Publishers.