Macroporous polymerized high internal phase emulsion (polyHIPE) flow cells were manufactured and used to extract caffeine from an aqueous solution using ethyl acetate. PolyHIPEs with a range of pore and pore throat mean diameters were synthesized by polymerization of water-hi-oil HIPE templates, which we produced by varying the agitation time of the emulsion template. It was observed that the overall mass transfer coefficient of the caffeine extraction was greater the smaller the mean pore throat diameter of the polyHIPE. The overall mass transfer coefficient within a polyHIPE was greater than in a blank tube and: spiral static mixer and was similar to that of a packed bed system but with a much lower pressure drop. The porosity of :the polyHIPE, did not affect the overall mass transfer coefficient, but polyHIPEs with higher porosity caused an increased extraction stage efficiency due to the increased residence time within the flow cell. It was: calculated that an interfacial area per volume of up to 17 600 m(2) m(-3) could be created between the aqueous caffeine solution and ethyl acetate within the polyHIPE flow cells, which is comparable to industrial extraction methods, such as mixer-settlers.