The Nuclear Medicine Department at Kent and Canterbury Hospital operates a limited weekend on-call service staffed on a rota basis by a technician, a nurse and a doctor. Following a review of the service over a 2-year period, a prospective study was carried out to analyse the workload of the on-call service from August 1991 to July 1992. The aim was to assess the impact of the service on patient management and examine the cost implications. Sixty-two scans were performed during the year (38 Saturday, 22 Sunday, 2 Bank Holiday) of which 52 were ventilation/perfusion (V/Q) lung scans. The study examined the reports on the scans and the subsequent course of treatment and changes in patient management. For V/Q lung scans, anticoagulation therapy was changed in 13 cases as a result of the scan report. Of the lung scans showing low probability of pulmonary emboli, four patients were discharged on the day of the scan and a further eight within 48 h. The total cost of the on-call service (staff and consumables) was 6020 pounds, i.e. less than 100 pounds per patient and less than 2% of the departmental budget. The low cost and high number of changes in patient management indicate a reasonable cost-benefit ratio.