The aim of the study was to elucidate the yield of annual chest X-ray and bacteriological examination in subjects with inactive tuberculosis or fibrotic lesions. Nearly 15 000 such persons registered at the Tuberculosis Clinics (C.B.s.) in Amsterdam, Rotterdam and Utrecht were allocated at random to either the Check-up group or the Discharge group: every person had an initial chest X-ray and examination of sputum or tracheal lavage for tubercle bacilli. Those in the Check-up group were re-examined annually for 3 years, while those in the Discharge group were not, but were encouraged to come to the C.B. if they developed symptoms suggestive of tuberculosis. Every patient was invited, after 3 years, to attend for a final follow-up examination. Nearly 90% of patients in the Check-up group attended for annual examination. Twenty-eight reactivations were reported during the 3 years, 23 pulmonary and 5 non-respiratory. They occurred in 12 patients previously treated by chemotherapy (1.2 per 1000 per year), in 15 with inactive tuberculosis (1.5 per 1000 per year) and in one with a fibrotic lesion (0.3 per 1000). Tubercle bacilli were found by smear and culture in only 2 cases and by culture only in 24. In the majority of reactivations only a small number of colonies were isolated on culture and no deterioration on the X-ray was seen. In the discharge group, 917 persons reported to the C.B.s because of pulmonary symptoms; 12 reactivations were found during the 3 years: 10 of the patients had received previous chemotherapy. Only 2 patients were positive at microscopy and in the majority of culture-positive cases a small number of colonies were isolated; 5 of the 9 patients with pulmonary tuberculosis showed deterioration in the X-ray appearance. At the final re-examination in the fourth year, similar numbers of cases were found in the Check-up group (14) and Discharge group (15). However, there were less smear-positive cases in the Check-up group and less cases with X-ray deterioration. There were 69 confirmed reactivations in all. The annual rate of reactivation was 1.6 per 1000 in the Check-up group and 1.1 per 1000 in the Discharge group. It is suggested that routine annual check-ups of patients with inactive tuberculosis or fibrotic lesions should be discontinued.