In a prospective, double-blind, placebo-controlled study, the efficacy and safety of acetohydroxamic acid (AHA) in preventing urinary calculogenesis was evaluated in 94 patients with chronic urinary infection. Stone growth occurred in 17% of the AHA group and in 46% of the placebo group (p less than 0.005). Completely reversible side effects consisting predominantly of psychoneurologic and musculo-integumentary symptoms were more prevalent in the AHA group (p less than 0.01). Side effects which were judged 'intolerable' were experienced by 10 (22.2%) of patients in the AHA group and 2 (4.1%) in the placebo group. It is concluded that AHA treatment is effective, relatively safe, and clinically useful in preventing infection-induced urinary calculogenesis.