One or more tuberculin skin tests (PPD) were carried out in 1865 members of the health care staff (71%) of the Hospital Clinic from Barcelona, so as to detect the prevalence of the infection and, particularly, to identify the converters (recently infected individuals) for the recommendation of antituberculous chemoprophylaxis. A higher number of converters was found in the group with higher risk of contagion owing to professional exposure, but the differences were not statistically significant. Significant differences were not found, either, between infected and noninfected individuals classified in risk groups. In the 1865 surveyed individuals, the initial and successive (when performed) PPD testings were negative in 987 (52%). In 775 individuals (41%), PPD reaction was positive in the initial testing. In the remaining 103 (5%), PPD reactions became positive after an initial negative result (converters). 50% of the 775 individuals with positive PPD reaction were over 35 years of age. The rate of infected individuals (positive PPD reaction) and converters was not significantly higher in those health care professionals with a supposed higher degree of exposure to infection.