Thermoresponsive microspheres of gellan gum-poly(N-isopropylacrylamide), i.e., GG-P(NIPAAm) semi-interpenetrating polymer networks (semi-IPNs) have been prepared by ionic crosslinking and used to study the controlled release (CR) of atenolol (ATL), an antihypertensive drug. Interaction of the drug with polymers was studied by Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry (DSC) was used to confirm the polymorphism and molecular level dispersion of ATL. Scanning electron microscopy (SEM) indicated spherical nature and smooth surfaces of the microspheres with some debris attached on their surfaces. Mean particle size measured by laser light diffraction ranged between 34 and 76 mu m. Equilibrium swelling performed at 25 degrees C and 37 degrees C in pH 7.4 phosphate buffer exhibited thermoresponsive nature of the polymers. In vitro drug release performed at 25 degrees C and 37 degrees C indicated temperature-dependency of ATL release, which was extended up to 12 h. In vitro release profiles at both the temperatures confirmed thermoresponsive nature of the polymers giving pulsatile trends. The % cumulative release data have been fitted to an empirical equation to estimate transport parameters and to understand the nature of drug release. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1832-1841, 2010