The original theory of Sampling with Partial Replacement (SPR) is modified to incorporate growth model projections of the unmatched plot data on the initial measurement. The Modified Sampling with Partial Replacement (MSPR) theory is illustrated by estimating growth and current volume using simulated plot data. In addition to the assumptions required by SPR, MSPR requires that the growth projection errors be random and have a mean of zero. If these assumptions are met, the modified theory improves the precision of the volume and growth estimators over the original SPR estimator. For. Sci. 42(3):328-334.