A solid-phase radioimmunoassay test employing 125I-labeled enterotoxin C and polystyrene tubes coated with specific antibody was used for the detection and quantitation of entertoxin C in condensed milk, cheddar cheese, custard, and ham salad. The assay was sensitive to 1 to 10 ng of toxin per g of food; nonspecific inhibitions were 16% or less.