A histological and ultrastructural study, coupled with transmission and scanning electron microscopy of the early changes in the liver following a single administration of cycloheximide (CHX), was carried out in male Wistar rats. At the histological level, apoptosis was already present in the liver 2 h after treatment. By scanning electron microscopy, the following sequential changes were observed: brightness and progressive detachment of hepatocytes from neighbouring cells, formation of surface infolds with multiple blebs and, finally, release of several membrane-bounded apoptotic bodies (ABs) in the extracellular space and into the sinusoidal lumen. Three hours after CHX administration, the apoptotic cycle was completed, as shown by the presence of phagocytosed ABs inside the cytoplasm of intact liver cells. Light microscopic examination of the liver 6 h after CHX administration showed ABs mainly located in the cytoplasm of intact hepatocytes and inside activated Kupffer cells. By transmission electron microscopy, it was possible to demonstrate that cells undergoing apoptosis were hepatocytes. At 24 h, the livers of treated animals appeared normal, with no evidence of apoptosis.