The use of growth promoters to fatten cattle, once widespread, is now banned or strictly regulated worldwide, with a view to protecting consumer health. The European Union, in particular, has issued directives, regulations, and guidelines for controlling such substances. Immunoassays (radioimmunoassays, ELISAs, biosensor assays) provide quick, sensitive, low-cost, and highthroughput screening tools for detecting steroids, corticosteroids, and β-agonists in live animals and meat. Their development has led, for instance, to eradication of the use of the dangerous compound diethylstilbestrol. Current challenges include the growing number of growth-promoting “black market” substances and the emergence of “cocktails” containing low levels of several mutually potentiating compounds. New analytical approaches, such as immunochemical multiplexing or the development of receptor-based assays, may contribute to meet these challenges.