Abstract: A method of preparing a sulfonamide-food color additive for detecting the presence of a compound such as a sulfonamide in animal feeds and pharmaceutical preparations for human or veterinary use involves admixing a minor amount of an approved food color additive with the compound in the presence of water and drying the resulting mixture to the desired form so as to incorporate the food color additive into the water of crystallization or other molecular structure of the compound. Upon being wetted, the resulting compound-food color additive produces a readily detectable color indicative of the presence of the compound. The method is particularly useful for detecting unacceptable levels of sulfonamides in animal feeds.