A case of fatal poisoning in a 1-year-old girl after ingestion of a household cleanser containing 4.5% sodium hypochlorite (Klorin) in an alkaline solution (pH 12.0) is reported. The forensic medical and toxicological investigations were supplemented by animal studies. These studies indicate that 5, 10, and 15 ml of Klorin/kg body wt given to rats is highly toxic, and that local tissue damage and secondary systemic involvement develops with a severity corresponding to the amount administered. The rats, all of which died, showed various degrees of degeneration and necrosis of the esophagoventricular mucosus membranes, changes analogous to those found at the autopsy of the child. A follow-up investigation of similar cases reported to the Swedish Poison Information Centre, during a limited time, was made to complete the picture.