The two major industrial sources of sulphur dioxide emissions are electrical generation and non-ferrous smelting. While flue-gas scrubbing and acid-plant technology are well established, continuous methods for the determination of SO2 in these process streams are based on expensive conventional UV or IR spectroscopic instrumentation in which the gases must be conditioned prior to analysis. Additionally, there appears to be no reliable continuous low-maintenance method of analysis for SO, in gases. Solid-state sensors for the continuous real-time measurement of concentrations of SO, and SO2 in process gas streams offer the possibility of monitoring the etkiency of flue-gas scrubbing, determining the concentrations of SO, in corrosion-susceptible ducting or in acid-plant conversion towers and guarding against excessive releases of SO, from acid-plant tail gas. The measurement of SO, and SO, in gases by solid-state electrochemistry is reviewed. The electrochemical cells are described, and wherever possible, the temperature and concentration ranges of the various solid-state devices reported in the literature are given. We conclude with a summary of the further requirements for a successful inexpensive commercial solid-state sensor for SO, and SO2 measurement in process gas streams.