AbstractIto cells, located in the space of Disse, extend their numerous long cytoplasmic processes to surround the sinusoidal wall. Conventional and immune electron microscopy demonstrates abundant microfilaments and a great amount of actin and myosin in these cytoplasmic processes. These morphological findings suggest the possibility of control of the sinusoidal circulation by their contraction. Two mechanisms may be involved in their contraction: namely nervous and humoral factors. Ito cells, often in close contact with the nerve endings, which contain many granules of substance P (SP), have numerous receptors for this peptide. Ito cells also have receptors for endothelin‐I (ET‐1), more commonly found in the periportal area of the hepatic lobule. Experimental studies using cultured Ito cells showed their contraction following treatment with ET‐1 or SP. These results suggest that Ito cells play an important role in the regulation of hepatic sinusoidal circul