Although bladder inflammation is known clinically to produce a variety of symptoms including urgency, frequency, and pain, there are only a few experimental studies that directly relate bladder inflammation with urodynamic and functional alterations. We have used the sensitized guinea pig model to study the effects of inflammation on micturition parameters, cystometry, and in vitro bladder contractility. This model depends on the allergic response of the bladder mucosa to ovalbumin, an otherwise non-irritative agent, as an antigen. In vivo exposure of the bladder to ovalbumin via urethral catheterization induced a prompt and marked increase in the number of micturitions in antigen-sensitized guinea pigs. Ovalbumin had no effects on the micturition parameters in the control group. Using in vivo cystometry, intravesical exposure to ovalbumin induced a significant decrease in both the pressure at which micturition was induced, and the volume at which micturition was induced. Ovalbumin had no effect on cystometric parameters of the control animals. In vitro exposure of whole-bladder preparations to ovalbumin induced a significant contractile response only in the bladders isolated from the sensitized guinea pigs. The responses of the isolated bladders to field stimulation and bethanechol were identical for bladders from both sensitized and control animals. In conclusion, exposure of the bladder to ovalbumin in the sensitized animal induced an increase in the frequency of micturitions and a decrease in the pressure and volume at which micturition was induced. Thus, intravesical exposure of the bladder mucosa to a substance that the bladder has been sensitized to can induce alterations in micturition that are consistent with the clinical symptoms of "urgency and frequency".