Acetaminophen (paracetamol) is an analgesic-antipyretic drug virtually devoid of typical anti-inflammatory activity and hence free of some of the side-effects of aspirin and related agents (e.g. gastric erosion and bleeding complications). The worldwide use of paracetamol as a household analgesic, including during pregnancy, prompted us to investigate its potentially deleterious effects in that setting. Pregnant rats were treated with paracetamol (150, 500 or 1,500 mg/kg, once a day by gavage) from the first day up to term pregnancy. In the group treated with the lowest doses, no histological changes were noticed in maternal and fetal livers or kidneys when examined under light or electron microscopy. With the higher doses, however, various dose-dependent effects of paracetamol were observed, namely necrotic areas of the liver seen with light microscope and further confirmed by electron microscopy. The kidneys revealed degeneration and necrotic foci under light microscopy with ultrastructural derangements. Electronmicrographs of the liver revealed hepatocytes bearing translucent bodies as a consequence of a dilated smooth endoplasmic reticulum. There were signs of necrosis both in the hepatocytes (lysis of mitochondria and presence of lipid droplets) and renal tissue (mitochondrial cytolysis in convoluted tubules). Our data point out the fact that both maternal and fetal tissues can be adversely affected by paracetamol.