Electrochromic (EC) glazing is now considered a viable alternative to fixed transmittance glazing. It has the potential to enable occupants to control daylight glare and solar heat gain without the use of blinds or external shading devices, giving users more access to daylight with all its inherent benefits. Furthermore, EC glazing can reduce energy consumption by decreasing cooling loads and electric lighting usage. Most research to date has studied the effects of EC glazing in scale models, computer simulations and full scale test rooms, and some of these studies have included human participants. However, there is a general lack of understanding regarding the performance and suitability of EC glazing in real-world working environments. A case study of the first UK retrofit application of EC glazing is being conducted in two adjacent offices in a university campus building. The offices are occupied by administration staff and have large southeastfacing windows. The existing double glazed units were replaced with commercially-available EC glazed units in 2012. Over a period of more than 18 months, the rooms were monitored intensively to record the effect of the EC glazing on both the physical room environment and the occupants themselves. A large amount of data from the monitoring programme is currently undergoing detailed analysis. Initial findings emerging from the installation and post-installation period are described in this paper.