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The colloidal probe technique (CPT) is used to measure distance-dependent interaction forces between polyelectrolyte layers physisorbed from 1 M NaCI solution in salt solutions between 0.1 mM and 1 M. Both linear polycations (poly(allylamine)hydrochloride, poly-1-lysine) and linear polyanions (poly(styrene-sulfonate)) are used. The repulsive interaction energies in the range between 10 -7 and 10 -4 J/m 2 are described by the theory of Alexander and de Gennes for surfaces covered with neutral anchored polymers. However, the brush thickness scales with molecular area and salt concentration with a power of -1/3 as known from a salted brush and reaches approximately 50% of the contour length in diluted solutions. The findings are confirmed by CPT images using a gold layer as height reference.