The purpose of this study was to evaluate the in- and expiratory pressures achieved by the use of different continuous positive airway pressure (CPAP) delivery systems. The study was performed on ten healthy adults breathing spontaneously with: 1) "simple CPAP", consisting of a fresh gas flow around 40 l/min and reservoir balloons of 2, 6 and 10 l and expiration against a water column, 2) a high-flow system CR60 CPAP, designed for home treatment and 3) another high-flow system Down's CPAP. Both high-flow systems used a venturi device (Downs Flow Generator, Vital Signs) giving flows around 90 and 170 l/min in our set-up, and the same PEEP valves (Vital signs) were used. All systems were tested with expiratory pressures set at 5, 10 and 20 cm H2O. Individual responses were found, but in general the simple CPAP with a 10 l latex balloon reservoir gave optimal CPAP. The high-flow systems were not found to provide better CPAP, however, CR60 CPAP was found also to be optimal with 5 and 10 cm H2O. Down's CPAP provided 3-5 cm higher expiratory pressure than the intended CPAP level. We recommend measurement of the pressure during the CPAP treatment to ensure that the intended CPAP is achieved.