Tonic immobility (TI) is a behavioral response to a sudden constraint and inversion in the rabbit. TI is characterized by a long-lasting immobilization, abolition of righting reflex, leg tremors, and waxy flexibility of the extremities. However, during TI autonomic functions do not seem significantly altered. We have used TI as a method to obviate the effect of anesthesia when recording urodynamic parameters during filling of the bladder. Our results suggest that, indeed, autonomic functions related to the filling phase of the micturition cycle are not altered by TI.