Six distinct forms of renin were found to be released from rat renal cortical slices incubated in vitro. The multiple renin forms were demonstrated using shallow gradient isoelectric focusing, and focused at pH 5.7, 5.55, 5.3, 5.15, 4.9 and 4.8. Before renal cortical slices were prepared, rats were given free access to both high- and low-salt diets containing, respectively, 0.2 or 0.005 mEq Na+/g food. Renal cortical slices prepared from rats maintained on the high-salt diet for 8 days (group I) released significantly different proportions of the six renin forms as well as less total renin when compared to rats first maintained on the high-salt diet for 8 days followed by the low-salt diet for 8 additional days (group II). In a second series of experiments, renal cortical slices prepared from rats maintained on the low-salt diet for 19 days (group III) secreted significantly different proportions of the six renin forms, as well as more total renin when compared to rats first maintained on the low-salt diet for 10 days, followed by the high-salt diet for 4 additional days (group IV). These studies demonstrate that the relative proportions of released multiple renin forms change when the kidney alters its renin secretory rate in response to changes in Na+ intake.