Human mast cells (HMC-1) take up anandamide (arachidonoyl-ethanolamide. AEA) with a saturable process (K-m = 200 +/- 20 nM, V-max = 25 +/- 3 pmol min(-1) mg protein(-1)), enhanced two-fold over control by nitric oxide-donors. Internalized AEA was hydrolized by a fatty acid amide hydrolase (FAAK), whose activity became measurable only in the presence of 5-lipoxygenase, but not cyclooxygenase, inhibitors. FAAH (K-m = 5.0 +/- 0.5 mu M, V-max = 160 +/- 15 pmol min(-1) mg protein(-1)) was competitively inhibited by palmitoylethanolamide. HMC-1 cells did not display a functional cannabinoid receptor on their surface and neither. AEA nor palmitoylethanolamide affected tryptase release from these cells. (C) 2000 Federation of European Biochemical Societies.