The development and evaluation of a two-week laboratory class, based on the diagnosis of human infectious diseases, is described. It can be easily scaled up or down, to suit class sizes from 50 to 600 and completed in a shorter time scale, and to different audiences as desired. Students employ a range of techniques to solve a real-life and relevant problem, and are introduced to the range and type of infectious agents, their routes of transmission and risk factors, clinical symptoms and diagnoses, and their treatment and prevention. No infectious material is used, and the practical is very inexpensive and easy to prepare. Six "patients" are diagnosed, using their symptoms, patient histories, temperature records, serology, blood and faecal slide examination, and bacteriological isolation from blood, faeces and cerebrospinal fluid.