Abstract: Micro-suspension polymerization is a technique that it is widely used on a commercial basis for the polymerization of vinyl chloride monomer into polyvinyl chloride. This invention reveals a greatly improved redox initiator system for use in such polymerizations. The redox initiator systems of this invention are comprised of (a) a free radical generator, such as a peroxide, and (b) a reducing agent selected from the group consisting of ascorbic acid, isoascorbic acid, and certain derivatives of ascorbic acid. The initiator systems of this invention do not require the utilization of water-soluble metal salts. However, water-soluble metal salts can be utilized in such initiator systems in catalytic amounts wherein the ratio of the water-soluble metal salt to the free radical generator is less than 0.09.