Blends of poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) were prepared by melt-blending and studied using a Monsanto rheometer, infrared spectrophotometer, and dynamic mechanical analyzer. The PVC/ENR blends were found to be self-crosslinkable, but immiscible at 25/75, 50/50, and 75/25 blend ratios. However, addition of a third reactive polymer, such as carboxylated nitrile rubber (XNBR), can make the ternary blend miscible. The quantity of XNBR required to make the binary blend miscible depends on the blend ratio of the binary PVC/ENR blend and increases as the binary blend ratio changes through 25:75 to 50:50 to 75:25. © 1993 John Wiley & Sons, Inc.