A method for the separation and quantitation of multiple forms of active renin in human plasma is described. Shallow gradient isoelectric focusing of plasma resolved active renin into seven distinct components in each of 10 healthy normal individuals. Plasma renin activity focused at isoelectric points of 5.71, 5.57, 5.47, 5.22, 5.08, 4.93, and 4.82 with corresponding proportions of 16.3, 15.4, 21.1, 20.3, 14.0, 10.0, and 2.5%. Silicon dioxide treatment of plasma significantly increased the yield of renin in the focusing gels. Although each individual plasma sample contained the same seven renin forms, there was variability in the relative proportions of the multiple renin forms between individuals. This variance was significantly greater than the variance introduced by the determination itself. The same seven active renin forms were also present in human renal cortical tissue. In conclusion, a method for the determination of multiple renin forms in plasma and renal cortical tissue is presented. At least seven active multiple renin forms were resolved in human plasma and renal cortex.