We have suggested that the renal tubular signal for renin release is related to alterations of sodium chloride cotransport in the TALH. Renin release is inhibited by increased sodium chloride transport and stimulated by interrupted sodium chloride transport. Because of the different affinities of the carriers for sodium and chloride, chloride rather than sodium is rate limiting for this cotransport process. Consequently, renin release is related to alterations of chloride delivery rather than sodium delivery to the TALH. The reduction of PRA by selective chloride loading and by short-term infusion of chloride salts is related to increased chloride delivery to the loop and hence increased chloride transport. Alternatively, chlorpropamide and antidiuretic hormone may inhibit renin release by increasing chloride delivery to the loop. Stimulation of renin release may likewise be related either to decreased chloride delivery and hence decreased transport in the loop (hypochloremia related to selective chloride deprivation) or to an intrinsic alteration in the transporting capacity of the loop (loop diuretics, potassium depletion, glucocorticoid deficiency, Bartter's syndrome). The intermediate steps between alterations of sodium chloride transport in the TALH and renin release remain to be defined.