Urodynamic investigations, including pressure studies, anal sphincter electromyography, and cystourethrography, done in young girls having symptomatic urinary infection show hyperreflexive activity of both striated sphincter and detrusor muscles, due to increased afferent input. In our series, this activity ranged froma a pattern similar to "uninhibited" bladder contractions, with normal voiding, to hyperactivity causing frequency, with voiding interrupted by frank sphincter spasms. The wide range and epidemiology of urinary infection in girls suggest that urethral dilatation (or urethrotomy) with long-term chemoprophylaxis is indicated only at one extreme--where the hyperactivity persists in the absence of infection. The role of persistent hyperactivity of detrusor and sphincter in recurrent urinary infection of childhood needs to be defined by a long-term longitudinal study; the high over-all recurrence rates of both covert bacteriuria and overt infection in girls still constitute a major medical problem.