The aim of this study was to investigate the stimuli-responsive behaviour of a pH- and temperature sensitive polymer system, i.e. a random copolymer of N-isopropylacrylamide and acrylic acid by atomic force microscopy (AFM). AFM allowed high resolution images of the physical states of the polymer chains at different conditions. Different collapsed and extended chain conformations of a random copolymer were seen over a wide range of pH and temperature. The shapes of both the individual copolymeric chains and globules can be clearly identified. Here we demonstrate the potential of AFM for characterising the stimuli responsive behaviour of such "smart" polymers. (C) 2000 Elsevier Science Ltd. All rights reserved.