In growing castrated pigs changes in the postprandial plasma zinc values were found to be inversely related to the zinc status of the animals. In pigs prefed with a moderate zinc diet (25 ppm) postprandial plasma zinc values increased, whereas in pigs prefed with a high zinc diet (150 ppm) values decreased after intake of a meal containing 150 ppm of zinc. It is considered that the presence of metallothioneine in the liver, which depends upon the zinc status, is responsible for this effect.