ABSTRACT: INTRODUCTION: The interdependence between endotoxemia, gram negative (GN) bacteremia and mortality has been extensively studied. Underlying patient risk and GN bacteremia types are possible confounders of the relationship. METHODS: Published studies with [greater than or equal to]10 patients in either ICU or non-ICU settings, endotoxemia detection by limulus assay, reporting mortality proportions and [greater than or equal to]1 GN bacteremia were included. Summary odds ratios (OR) for mortality were derived across all studies by meta-analysis for the following contrasts; sub-groups with either endotoxemia (group 3), GN bacteremia (group 2) or both (group 1) each versus the group with neither detected (group 4; reference group). The mortality proportion for group 4 is the proxy measure of study level risk within L'Abbe plots. RESULTS: 35 studies were found. Among 9 studies in an ICU setting, OR for mortality was borderline (OR < 2) or non-significantly increased for groups 2 (GN bacteremia alone) and 3 (endotoxemia alone) and patient group 1 (GN bacteremia and endotoxemia co-detected) each versus patient group 4 (neither endotoxemia nor GN bacteremia detected). The OR's were markedly higher for group 1 versus group 4 (OR 6.9; 95% CI, 4.4 - 11.0 when derived from non-ICU studies. The distributions of P aeruginosa and E coli bacteremias among groups 1 versus 2 are significantly unequal. CONCLUSIONS: The co-detection of GN bacteremia and endotoxemia is predictive of increased mortality risk versus the detection of neither but only in studies undertaken in a non-ICU setting. Variation in GN bacteremia species types and underlying risk are likely unrecognized confounders in the individual studies.