An light and electronmicroscopic study of the rabbit hepatocytes during shock after experimental histamine release by Polymyxin-B-sulphate was made. As soon as five minutes after the histamine liberation the endoplasmatic reticulum becomes dissociated and the mitochondria show a spherical transformation. When the shock lasts up to one hour the changes are more intensive. The rest of deteriorated mitochondria and the endoplasmic membranes are expelled from the cells into the sinusoid lumina in form of myelinic figures. The hepatocyte microvilli swell up at first, and later, from the fifteenth minute after the beginning of shock they disappear which results in the flattening of the plasma membrane or its complete dissapearance in some places. Endothelial cells suffer similar alterations and they also acquire cytoplasmic protrusions. The findings lead to the conclusion that the changes of hepatocytes during shock after histamine liberation are primarily due to the direct influence of released histamine, and secondarily to the influence of hypoxia produced during the shock state.