A great part of the world's population is cared for by rural health workers who are also collecting data for epidemiological studies. These workers have a low level of medical training and are working in a poor technical environment. At the request of an international humanitarian and medical organization (Médecins Sans Frontières), we have developed an integrated (hardware and software) system, TROPICAID, based on a hand-held computer and designed to increase rural health workers' efficiency. The software is easy to use and enables users to get information from an internal data base on 60 drugs. The decision-making module analyzes the patient's parameters (460 different symptoms are recognized) and indicates possible diagnoses (the system knows 210) and relevant treatments. In addition, the system facilitates the collection of medical data for elementary statistical analysis. The computer, which is lightweight (1.5 kg) and compact, runs on battery power for up to a week in normal use. The program which is written in Pascal and data are stored in high-capacity EPROMs. An early trial in Chad with Médecins sans Frontières has shown the value of such a project as well as a few weaknesses to be overcome.