The results of a process evaluation of the epidemiological surveillance activities in 948 health units, situated in 98 of the most populated cities of each State in the country are presented. The survey was conducted towards the end of 1985. The following aspects were analyzed: information system, data analysis, epidemiological investigation. Institutional insertion, vaccination activities, management aspects and capacitation of the health worker were considered as potential determinants of performance. Data were submitted to correspondence analysis and a process of ascendant hierarchical classification, using the statistical package "Systeme Portable Pour L' Analise de Données-SPAD". The performance pattern was not found to be homogeneous. Six different classes of epidemiological surveillance practice in the health units were observed. In 53.7% of the services visited, even the most elementary norms of activity were not complied with. The presence of vaccination activities in the health units was associated with better performance in epidemiological surveillance. The study points to the need to review the epidemiological surveillance model in use in Brazil. It is no longer acceptable to restrict the practice of epidemiology in health services to communicable diseases, now to manage programs and services without epidemiological information.