This presentation discusses the application of an in-line spectroscopic technique during the process development stage of the production of a pharmaceutical intermediate in a continuous mixer. Specifically, we will show the development and implementation of a transmission NIR measurement system to monitor the composition of a multi-component process stream in real time. These real time data are used during process development to facilitate scale up, and to assess ability of the process to dampen input noises. Additionally during developmental processing this measurement system is used for real time process monitoring and detection of process upsets.