Voltage-gated K and Ca currents were recorded in acutely dissociated neuroendocrine cells of the supraoptic nucleus. The effect of repeated activation of the currents by trains of (10) voltage pulses over a range of pulse-repetition frequencies were examined. There was a significant reduction of K-current amplitude and a significant increase of Ca-current amplitude during trains with high repetition frequencies. Frequency-dependent changes in K and Ca conductances may contribute to frequency-dependent spike-broadening which is exhibited during bursts of action potentials generated by these neurons.