Communication: pH-Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8. Permeation and encapsulation of FITC-dextran (MW 75 000) into polyelectrolyte multilayer capsules. Top: pH 10, center: pH 3, bottom: pH increased to 10 after the capsules were loaded with FITC-dextran at pH 3. The bulk FITC-dextran was removed by washings at pH 10.