Massive elevation of intra-abdominal pressure (IAP) causes renal, cardiovascular, and respiratory dysfunction. Positive end-expiratory pressure (PEEP) markedly increases the detrimental effect of IAP on the cardiovascular system. The purpose of this study was to determine the effect of PEEP on IAP. In 15 patients requiring mechanical ventilation, IAP was measured, after 15-minute equilibration intervals, at PEEP levels of 0, 5, 10, and 15 cm H2O. Parametric analysis with multiple paired t tests and nonparametric analysis with Spearman's rho and Kendall's tau tests were used to determine correlation between PEEP and IAP. All patients were male. The mean age was 39 years (range, 18-77). Ten patients had just had laparotomy. No correlation was found between PEEP and IAP. We conclude that PEEP of 15 cm H2O or less has no effect on IAP, and we discuss the clinical implications.