Experimental investigations were conducted for single-phase liquids to determine interstage backmixing rates in an agitated, fully baffled, 24-cm-diameter, two-stage, compartmented column. The backmixing rate was indirectly determined by introducing a tracer into one stage and then measuring the tracer concentration with time in both compartments as the tracer migrated from the injected stage to the noninjected stage. A transient tracer mass balance on both compartments allowed the use of the transient experimental tracer concentration to determine the interstage backmixing rate. The effect of flow through the column on interstage, backmixing was determined. Experimental and correlational results are reported here for two interstage openings: (1) a center hole and (2) a centered draft tube. Two impellers were tested: a six-bladed disk (6BD) impeller and a high-efficiency impeller (the Chemineer HE-3). The data were correlated in dimensionless form, and predictive methods are presented that allow the prediction of the interstage backmixing rate as a function of (a) the impeller type, (b) fluid properties, (c) the interstage opening geometry, and (d) the forward flow rate. The correlations for the effect of the forward flow rate on backmixing allow the design of a compartmented column, using a draft tube attached to a center hole opening, which has no backmixing. Thus, a compartmented column can be designed and operated as a series of continuous stirred reactors (or compartments) in series, without any interstage backmixing.