The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly(styrene sulphonate), and the polycation, poly(allylamine hydrochloride), onto melamine formaldehyde resin latex of 5 microm diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH 1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 10(4) N/m2. However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 10(6) N/m2.