The 3-year experience of setting up a control programme for measles in a developing community has been used to devise an extended problem-solving exercise in clinical epidemiology for 4th-year medical students. Following the same steps taken by health workers and using the maps, sociodemographic and measles incidence data available to health workers in the programme, students proceed through five self-contained but interconnected modules or‘rings’. These rings cover disease management, surveillance, mass campaign, community-based surveys and finally implementation of changes in the health service. The first 3‘rings’of this exercise were run on five groups of 20 students during 1992 in what has been regarded as a development phase to eliminate obvious‘bugs’and blind loops and to define the correct level of detail for each question. A description of the objectives and process of this learning exercise and its possible future applications is presented.