In order to determine the value of routine pre-operative screening investigations, the medical notes of 100 patients undergoing elective surgical procedures under general anaesthesia were subject to prospective audit. Pre-operative screening investigations (full blood count, urea and electrolytes and random glucose) were analysed in terms of frequency of abnormalities and whether or not the peri-operative management was changed when the result was abnormal. The frequency of results being present in the note at the time of operation and the costing of the tests was also examined. A total of 773 tests was performed of which 70 (9.1%) were abnormal. Peri-operative management was altered as a result of only two abnormal results (0.2%). Eight complications arose, none of which could have been predicted by the pre-operative screening tests. In only 57% of cases were the results present in the medical notes at the time of surgery. It is conservatively estimated that a saving of pound 50 000 per year could be made in our hospital alone by selective ordering of tests.