A new mode of jet ventilation, high frequency two-way jet ventilation (HFTJV) was devised and introduced to increase carbon dioxide elimination during jet ventilation. Its ventilatory efficiency and features were investigated and compared with those of high frequency jet ventilation (HFJV) in 10 patients with normal cardiopulmonary function. Random sample selection and randomized cross-over trial were used for comparison between HFTJV and HFJV at the same ventilatory settings of driving pressure 1 kg/cm2 (14.22 Psi), respiratory rate 100/min and I/E ratio 1:2. Peak inspiratory pressure (PIP), end-expiratory pressure (EEP) and main variables of air blood gas analysis (PaO2, PaCO2, pH) were measured and recorded during the use of HFJV and HFTJV. PIP and EEP were significantly lower than with HFTJV than with HFJV. EEP of HFTJV showed a slightly negative pressure (-0.17 +/- 0.03 kPa). PaCO2 with HFTJV was significantly lower than that with HFJV, but PaO2 and pH with HFTJV were significantly higher than those with HFJV. HFTJV was shown to have a ventilatory feature of decreasing airway pressure and simultaneously increasing carbon dioxide elimination, as compared with HFJV. Whether this ventilatory feature of HFTJV can be utilized for various respiratory support in patients with abnormal cardiopulmonary function needs to be further studied.