The effect of noradrenaline (NA) on voltage-sensitive calcium currents in neuroblastoma x glioma hybrid (NG108-15) cells has been studied using a whole-cell clamp technique. NA inhibited calcium current. The EC50 for NA induced inhibition was 177 nM. The NA receptor involved had a similar pharmacological profile to alpha2 adrenoreceptors but did not respond to clonidine. NA inhibited calcium current by an amount which dependend on both membrane potential and current amplitude. When current-dependent inactivation of calcium current was maximal, NA was without effect. The data are consistent with a mechanism where NA enhances current-dependent inactivation.