Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes have been grown by surface-initiated atom transfer radical polymerization (SI-ATRP) from the gold-water interface at different grafting densities, and neutron reflectivity has been used to characterize the response of the brush structures to changes in pH and temperature. Low-density brushes show the greatest response to changes in pH, with the swelling of the highest density brushes essentially independent Of pH. The Scaling exponent of the swelling ratio with grafting density changes from beta similar to -0.7, which is typical for neutral brushes, at pH 10, to. beta similar to -1.4, at pH 3, reflecting the change in the dominant contribution to the osmotic pressure in the brush. At low pH, the osmotic pressure due to the counterions of the charged segments exceeds that of the segmental excluded volume, except in the highest density brushes, resulting the pH-dependent swelling response of all but the highest density brushes. At pH 10, increasing temperature causes a partial collapse of the brushes With a transition temperature in, the range 30-40 degrees C. The transition is associated with the dehydration of the hydrophillic segments. The magnitude of the deswelling decreases with increasing grafting density, reflecting the decreasing Volume fraction of water in the brush.