Since 1973 the University Children's Hospital of Freiburg has provided a service devoted to selective screening for inborn errors of metabolism with particular emphasis on organic acidurias. Patients to be investigated are preselected by local clinical paediatricians. Between 1973 and the end of 1990, 46,700 specimens from approximately 40,000 patients were screened by the methods listed in Table 1. A total of 464 cases were found consisting of 51 different diseases, 242 cases of 23 different organic acidurias and 222 cases of 28 other inborn errors of metabolism. The number of cases diagnosed parallels the number of patients investigated showing that there is still a real demand for metabolic screening. The number of children to be investigated is steadily increasing. Using the presented and already published data an appraisal of the overall incidence of all organic acidurias (1:6700) has been made as well as of the frequencies of the most common types of these disorders.