Animal experiments have shown that quinolones can cause irreversible damage to cartilage in strained joints of young animals. Since a similar effect in humans cannot be excluded, the new quinolones are contraindicated in children and pregnant women. Nalidixic acid was the first quinolone developed and was often used in pediatric patients for the treatment of urinary tract infections. This compound is also known to cause damage to juvenile cartilage in animal studies but is still licensed for pediatric use. In three different retrospective studies of children treated with nalidixic acid, no case of quinoloneassociated arthropathy could be detected by careful X-ray examinations or comparisons with control patients. This disparity most probably can be explained by interspecies differences: human cartilage may be insensitive or only slightly sensitive to the arthropathic effects of quinolones. Careful prospective evaluations of the efficacy and safety of new quinolones in childhood infections are both medically indicated and ethically justified.