The interrelationship between arginine and calcium in glucagon release was studied using the in vitro perfused rat pancreas. In the presence of a normal 2 mM calcium concentration, 10 mM arginine provoked biphasic glucagon release, the amplitude of such a response being inversely related to the glucose concentration of the perfusate. At the lowest 3.3 mM glucose concentration, and after prolonged (40 min) as well as short (10 min) periods of calcium deprivation, arginine-induced glucagon release was inhibited. These results clearly indicate that calcium is necessary for either the recognition or effectiveness of arginine as a stimulus to the alpha-cell. Taking into account this, as well as other data presently available in the literature, it is suggested that calcium plays a versatile role - permissive, inhibitory and stimulatory - in glucagon secretion. The intimate mechanisms by which calcium exerts such versatile actions in the alpha-cell remain to be elucidated.