Author for correspondence: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan Tel.: +81 3 5841 4768 Fax: +81 3 5841 4768 seiichi@mol.f.u-tokyo.ac.jp Temperature is the most important physical property for living organisms. This importance is easily understood, as we utilize body temperature as a simple indicator of our health status. The health status of all organisms is inf luenced by countless chemical reactions occurring within their cells. All such intracellular chemical reactions are accompanied by either heat release (exothermic) or heat absorption (endothermic), resulting in spatial temperature variation within the living cell. This local temperature variation could affect certain cellular functions, such as gene expression, protein stabilization, enzyme–ligand interactions and enzyme activity [1]. Thus, intracellular thermometry, a new method of cell monitoring, could provide information regarding the status of the living cell, and ultimately, information regarding the status of the entire body. For an accurate and meaningful measurement of intracellular thermometry, a thermometer with several specific capabilities is required. It should be small in size, exhibit a high temperature resolution (i.e., high sensitivity) and demonstrate high spatial resolution, low toxicity and functional independence from other intracellular environmental factors, such as pH and ionic strength. For sensors with a high spatial resolution, a fluorescent probe is an obvious choice and recent developments in novel fluorescent molecular thermometers have opened the door to intracellular thermometry methods [2,3]. In particular, the fluorescent polymeric thermometer (FPT), which we developed, has successfully revealed the intracellular temperature distribution in combination with fluorescence lifetime imaging microscopy (FLIM) [4]. In this editorial, we briefly summarize the recent advances in