Abstract The effects of extracellular application of arginine vasopressin (AVP) upon membrane currents in L6 skeletal myocytes was investigated using the whole-cell configuration of the patch-clamp technique. At O mV AVP produced large amplitude, transient outward currents that reversed when the clamping potential was changed to −100 mV (negative to E K) The effects of alterations in the extracellular K + concentration upon the current reversal potential suggested that the current elicited by AVP was carried mainly by K + ions. Intracellular dialysis with 10 μM inositol 1,4,5-trisphosphate (InsP 3) elicited similar currents but only in 6/14 cells. Inclusion of 5 mg ml −1 heparin in the intracellular solutions was ineffective at inhibiting the current responses to AVP. The AVP-induced current was totally abolished when the intracellular EGTA concentration was increased from 0.05 mM to 10 mM or Ca 2+ was removed from the extracellular perfusing solution. These results suggest that AVP produces activation of a Ca 2+-sensitive K + conductance in L6 skeletal myocytes by a process dependent upon extracellular Ca 2+ and not intracellular Ca 2+ release.