In 2 field mortalities studied, sheep died and showed haemorrhage and diffuse liver necrosis after drinking water from dams containing growths of the blue green algae Nodularia. Sheep dosed with water containing N. spumigena Mert 5, 9 and 18 days after collection from one of the farm dams developed pyrexia and leucopenia before death. At necropsy, these sheep showed extensive haemorrhage, accumulations of yellow fluid in body cavitis and acute hepatic necrosis. Guinea pigs dosed with the water 9 days after collection died and developed periacinar liver necrosis, but those dosed 12 days after collection did not.