Intravesical instillation of xylene (30-50%) produced detrusor hyperreflexia characterized by a decrease in both the bladder capacity (time to micturition in the cystometrogram) and the urine volume in conscious rats placed in a restraining cage. At this time, the bladder tissue showed evidence of experimental cystitis with degradation of the epithelium and edema and hemorrhage in the submucosa, and a slight increase in the content of prostaglandin E2, which stimulated directly and/or indirectly capsaicin-sensitive sensory fibers. In addition, the bladder exhibited high amplitude spontaneous activity, but the bladder contractions induced by acetylcholine, substance P, prostaglandin E2 and capsaicin were not changed following intravesical instillation of xylene. In these hyperreflexic rats, atropine suppressed the amplitude of the micturition contraction and morphine increased the bladder capacity at similar doses as in sham-treated rats, while thiopental and indomethacin increased the bladder capacity at lower doses than in sham-treated rats. These findings indicated that intravesical instillation of xylene had produced detrusor hyperreflexia in conscious rats, and that the detrusor hyperreflexia is thought to be a useful model for evaluating the effect of a newly-developed agent on bladder function.