In situ spectroscopic ellipsometry (SE) has been used to monitor growth of SiGe/Si epitaxial layers with box or step-graded Ge composition profiles. Real-time estimates of both Ge concentration and layer thickness have been made as a function of time. Estimates of Ge concentration are generally accurate, but total thickness is often under-estimated when very thin incremental surface layers are analysed. Interface grading observed when gases are switched into the reactor is shown to depend on the presence of hydrogen in the mixture. A new algorithm for analysis of real-time SE data, which allows prior knowledge about the growth system to be used in process control, is described.