The respiratory states of 36 consecutive Nigerian patients undergoing surgery and anaesthesia had been studied in the pre-operative, para-operative and post-operative periods. The respiratory function of most of the patients was quite good. In patients who received general anaesthesia, the Pa02 values were found to be significantly higher during anaesthesia than pre-operatively or post-operatively. Post-operatively the Pa02 values were slightly lower than the pre-operative values; hypoxaemia was rarely found but a few patients had Pa02 levels of 10-20 mm Hg lower than the pre-operative levels. The PaC02 levels during and after anaesthesia were within normal limits except in a few of the patients under halothane anaesthesia who showed a mild degree of hypercarbia, and a few of some of those on controlled ventilation who demonstrated hypocarbia. The pH changes paralleled the PaCO2 changes generally. The patients operated upon under epidural block, showed the least changes in blood gases.