Quindoxin (quinoxaline-1,4-dioxide), a former 'growth promoter' used in animal husbandry, has been taken from the market because of its photoallergic properties. Quindoxin increased the live weight gain in young chickens, pigs, and poultry. Quindoxin showed little antibacterial activity in vitro against common gram-positive or gram-negative species under aerobic conditions, but its activity was 10-100 times greater under anaerobic conditions. Under anaerobic conditions, Quindoxin inhibited the growth of Staphylococcus aureus and Escherichia coli. Quindoxin derivatives olaquindox and carbadox have been used as feed additives for growth promotion in pigs, rabbits, and other animals. It is extremely difficult for breeders to avoid exposure to dust containing relatively high concentrations of olaquindox. A very low dose of olaquindox produces contact dermatitis mainly by phototoxic or photoallergic mechanisms.