We measured the effects of dissociating inspiratory and expiratory positive pressure (PI and PE, respectively) on the inspiratory flow limitation pattern and on genioglossus (GG) activity in nine sleep apnea patients. Measurements were made at two different levels of PI with stepwise increases in PE. Flow-limited breaths were observed during each recording session. In six of nine subjects, maximal inspiratory flow (I_max) was correlated with the difference between PI and PE (correlations were negative in 5 subjects, positive in 1 subject). In three other patients, I_max was not influenced by the amount of pressure difference. A positive relationship between tonic and/or phasic GG electromyographic activities and PI-PE difference was observed at least at one PI level in all patients. This correlation was observed independently of the presence or absence of any relationship between I_max and the amount of pressure difference. Our results suggest that increasing the PI-PE difference (i.e., decreasing PE) may be associated with a significant worsening in inspiratory flow limitation and that the I_max-pressure difference behavior is not dependent on the GG electromyographic-pressure response.