Photocatalysis and electroanalysis are two seemingly disparate research areas, but they are linked by the fact that both involve the use of well-known materials, TiO2 and diamond, respectively, in new ways in the service of both environmental and medical sciences. In the present article, recent developments in the area of TiO2 photocatalysis and diamond electrochemistry are summarized, with emphasis on our findings at the University of Tokyo. In the photocatalysis section, we present the fundamental aspects of TiO2 photocatalysis and its practical applications, including ail purification, self-cleaning surfaces and transparent superhydrophilic coatings. The diamond electrochemistry section deals with the electrochemical characterization and applications of diamond electrodes, which exhibit high sensitivity and excellent stability For electroanalysis, in contrast to conventional electrode materials. A particularly interesting environmental application of diamond electrodes has been developed, this involves the trace analysis of lead without the use of mercury.