Twenty-three new cases of pulmonary tuberculosis were notified among 21,951 National Health Service staff working in the Lothian area during the 6 years 1978-1983. Eight of the 23 cases were detected by pre-employment screening. Five further cases were detected during employment by voluntary chest X-ray screening. During the same period a further 10 cases presented with symptoms, suggesting that voluntary screening during employment was relative unproductive in the detection of new cases. There was no evidence of an increased risk of pulmonary tuberculosis in most occupational groups of Health Service staff; the average annual incidence during employment was 11/10(5) overall with 9/10(5) in nurses and 23/10(5) in doctors, rates very similar to the local population of working age. However two cases occurred in 300 medical laboratory technicians giving a much higher incidence of 111/10(5) (p less than 0.005).