Multiple water-in-oil-in-water (W/O/W) emulsions for drug delivery systems were produced by extruding a coarse W/O/W emulsion five times under pressure of 70-150 kPa through Shirasu Porous Glass (SPG) membrane with a mean pore size of 5.4, 7.6, 10.7, 14.8, and 20.3 mu m. The encapsulation efficiency of a marker (CaNa2-EDTA) determined by inductively coupled plasma (ICP) emission spectrophotometer was 83-85% in the emulsion products containing 30 vol.% of inner droplets and 30-50 vol.% of outer drops. The ratio of mean particle size to the mean pore size after five extrusions decreased from 1.25 to 0.68 as the pore size increased from 5.4 to 20.3 mu m at the wall shear stress of continuous phase in the pores of 200 Pa. The mean particle size of the resultant droplets decreased with increasing the continuous phase viscosity and with decreasing the pore size. The ratio of mean particle size to the mean pore size for the same multiple emulsions prepared by direct extrusion of W/O emulsions through SPG membrane into stirring continuous phase was 3.46 and was independent on the pore size. At low continuous phase viscosity, uniform droplets with a span values of 0.28-0.34 were produced at very high transmembrane fluxes exceeding 200 m(3) m(-2) h(-1). (c) 2006 Elsevier B.V. All rights reserved.