Kainate evokes a non-desensitizing membrane depolarization in neuropile glial cells of the leech Hirudo med- icinalis. We measured membrane potential and intracellular pH, pH:, using double-barrelled pH-sensitive microelectrodes, and intracellular calcium, Ca2+i, using the change in fluorescence ratio of intracellularly injected fura-2, in these glial cells in situ. 20–50 μM kainate produced a depolarization of 18–28 mV and a decrease of pHi by 0.27 ± 0.07 pH units. Ca2+, increased by 306 ± 128 nM upon kainate, which could be inhibited by the non- NMDA antagonist CNQX. Glutamate (0.1 mM) also produced a fall in pH, and a rise in Ca2+i, which were however, much smaller. Quisqualate and N-methyl-D-aspartate had only small or no effects on membrane potential, pHi or Ca2+i. It is concluded that leech neuropile glial cells have a kainate-type glutamate receptor, which mediate significant transients of intracellular H+ and Ca2+.