Commercially available blood-collection tubes may be contaminated with endotoxin (315 +/- 95 pg/tube) and could therefore be unsuitable for blood collection for endotoxin measurement. Plasma separation and storage are a potential source of contamination. To avoid contamination and error, we have developed new blood collection tubes that contain heparin free of endotoxin (LPS) and a gel to separate plasma and blood cells. The LPS content is less than 4 pg/tube. Samples can be stored and frozen without plasma withdrawal to preclude contamination. LPS recovery experiments have shown that the new blood-collection tubes do not bind LPS to the separation gel or vial wall. With these tubes, in vitro formation of tumor necrosis factor (404 +/- 163 ng/L in standard tubes vs less than 40 ng/L in special collection tubes) is minimized.