Polymerisation of acrylic acid has been initiated by the sodium metabisulphite/potassium bromate redox pair. The reaction occurred in aqueous drops dispersed in a paraffinic oil and stabilised by a non-ionic surfactant. Characterisation of drop/particle behaviour throughout the course of polymerisation, using a freeze-fracture technique with a scanning electron microscope, suggested a mechanism of drop polymerisation that included continuous and simultaneous drop coalescence and break-up. The important role of drop mixing in the polymerisation was investigated by conducting polymerisations with some varied experimental parameters. It has been found that the agitation speed, the composition of the reductant aqueous solution and the method of adding the aqueous reductant had significant effects on polymerisation rate, limiting monomer conversion, particle size and size distribution in the final latexes.