||An improved skin window chamber technique has been developed and used for a quantitative study of the chemotactic effect of leukotriene B4 (LTB4). LTB4 (0.5 microM) was exposed to a skin window on the forearm of eight healthy volunteers, while phosphate buffered saline served as control in a skin window on the other forearm. Skin window exudates and samples of blood draining the skin window areas were collected after 1, 2, 4, 8, and 24 h. The samples were quantitated for the different types of leukocytes as well as the intra- and extracellular concentration of the eosinophilic cationic protein and lactoferrin as markers of eosinophil and neutrophil granulocytes. A significantly increased migration of neutrophil granulocytes into the skin window chamber containing LTB4 was found from the 2nd to the 8th hour after the initial LTB4 exposure. The eosinophils reached a significant peak at the 4th hour. The rise in the actual number of eosinophil cells did not reach significance, whereas measurements of the eosinophilic cationic protein in the cellular fraction of the exudate exhibited a significant increase as a reflection of the number of eosinophils. This highlights the potential clinical value of eosinophilic cationic protein measurements to reveal eosinophilia instead of the traditional eosinophil counts. Extracellular eosinophilic cationic protein and lactoferrin did not change significantly in the LTB4-exposed skin window, implying that LTB4 does not activate the eosinophils and neutrophils to exocytosis of their enzymes. The present in vivo results support the concept of LTB4 being a potent chemoattractant to neutrophil and less so to eosinophil granulocytes in humans, a chemoattractant that recruits the leukocytes but does not seem to activate them.