The effect of increasing pneumatic splint pressure on cutaneous oxygen tension measured transcutaneously (TcPO2) was investigated in 12 subjects. The mean initial TcPO2 was 70.6 mmHg. TcPO2 decreased linearly on increasing the pressure within the splint. TcPO2 became zero at a mean splint pressure of 28 mmHg. Second, three accepted methods used by the ambulance crew to assess inflation pressures of the splint were investigated and found to be unreliable. In the light of these findings the risk of ischaemic complications as a result of applying pneumatic splints to a fractured limb is discussed. We advocate a recommended maximum splint pressure of 15 mmHg and that the splint should be manufactured with a security blow-off valve set at 15 mmHg.