Limulus amebocyte lysate (LAL) assay and gas chromatography-mass spectrum (GC-MS) analysis are usually used for the quantification of lipopolysaccharides (LPS) from the environment. The LAL assay measures endotoxin units to represent the LPS biological function but GC-MS analysis measures decanoic (C-10:0) and dodecanoic (C-12:0) 3-hydorxy fatty acids (3-OH FA) concentration to represent the LPS chemical composition. A study was carried out using these methods to evaluate their degree of correlation. Using the culture supernatants of 30 independent strains of Pseudomonas aeruginosa, the bacterial supernatants gave of 0.53 +/- 0.45 and 2.49 +/- 1.75 mg/l of C-10:0 and C-12,C-0 3-OH FA, respectively, compared to 17.96 +/- 113.28 mg/l of LPS with the LAL assay (1 ng/ml of LPS congruent to 0.78 EU/ml). The 3-OH FA concentration relative to the endotoxin unit dose in the supernatants exhibited a positive correlation (r(2) = 0.5182, C-10:0; r(2) = 0.4359, C-12:0). When supernatants having a high level of endotoxin were used to treat peritoneal exudates cells, nitric oxide (NO) was generated in a dose-dependent manner (r(2) = 0.6174). To deternime if either C10,0 or C12,0 3-OH FA can act as an indictor of LPS quantity was correlated with this immunostimulatory effect, the correlation of these 3-OH FA concentrations against the produced No levels was evaluated. This also exhibited a positive correlation; however, the two indicators of 3-OH FA gave different dose-responsible performances (r(2) = 0.3211, C-10:0; r(2) = 0.4527, C-12:0) (c) 2006 Elsevier B.V. All rights reserved.