The U.S. Food and Drug Administration (FDA) announced they had identified melamine, a substance used as a fertilizer and in the production of plastics, such as kitchenware and whiteboard surfaces, in tested samples of recalled pet food from Menu Foods. The substance was also identified in urine and tissue samples taken from sickened cats and from the kidney of one cat that had eaten the recalled food.

Melamine is primarily used in Asia as a fertilizer but is not approved for that use in the United States. It is used in plastic kitchenware in this country.

On March 23, New York State Agriculture Commissioner Patrick Hooker and Cornell University's College of Veterinary Medicine Dean Dr. Donald F. Smith announced that scientists had identified aminopterin as a toxin present in samples from Menu Foods.

In today's press conference, however, Dr. Stephen Sundloff, director of the FDA Center for Veterinary Medicine, said that no independent testing laboratory has confirmed aminopterin in tissue or food samples. Tests conducted by a Menu Foods client, the FDA, and Cornell University have all identified melamine, Dr. Sundloff said, and the FDA is no longer focusing on aminopterin.

The FDA stated that data concerning melamine toxicity in animals is lacking and cannot be certain it is linked to the illness or deaths of animals eating the recalled foods. The FDA recommends that existing protocols on treating pets affected by the recalled food is the best course of action.