An appropiate experimental study was designed and carried out in mongrel dogs, in order to evaluate the active muscle and cholinergic participation on bladder compliance. The filling bladder pressure was measured at 100 ml of bladder volume, in 50 dogs distributed into five groups of 10 dogs each: (1) control group, (2) group which received atropine (cholinergic antagonist), (3) group which received verapamil (extracellular Ca2+ blocker), (4) group which received nitroprusside (intracellular Ca2+ antagonist), and (5) group which received EGTA (Ca2+-chelating agent). Furthermore, the following was demonstrated. (1) The greatest decrease of the bladder filling pressure was observed in the group which was treated with EGTA. (2) A significant decrease of the bladder filling pressure was also seen in the group which was given nitroprusside. (3) The decrease of bladder filling pressure in the verapamil group tended towards statistical significance. (4) There was no decrease in the atropine group. Thus, it was concluded that the active muscle component has an important role in the bladder compliance (through the intracellular calcium fraction), and the cholinergic component does not participate in the bladder compliance.