The first total synthesis of the5(S)-hydroxy-10,11-dihydro-12-oxo-6(Z),8(E),14(Z)-eicosatrienoicacid(10,11-dihydro-12-oxo-LTB4) (3) isreported. This compound is a key pivotal intermediate inthebiotransformation of LTB4 by the so-called“LTB4 reductase pathway”.