The behavior of the emulsifier sodium dodecyl sulfate and electrolyte sodium hydroxide was studied at the oxidation stage and beyond in the emulsion polymerization of methyl methacrylate initiated by the manganic hydroxide–hydrazine hydrate system. From the rate of polymerization and from the adsorption of hydrazine it was shown that addition of emulsifier is more effective at the oxidation stage than after. But the reverse is obtained with the electrolyte. The effect of hydrazine concentration was also studied. The results are explained on the basis of a surface reaction between hydrazine hydrate and the insoluble manganic hydroxide.