The bradykinin relaxation of the acetylcholine-contracted guinea-pig ileum is decreased by increasing the concentration of acetylcholine. This finding prompted an investigation to determine whether other spasmogens can reduce the bradykinin relaxation, and the mechanisms involved. Linear inverse relationships were found between both the percentages of maximum contraction and concentrations of histamine and eledoisin, and the bradykinin relaxation. Eledoisin and histamine showed smaller regression equation slopes than acetylcholine. No relationship existed for angiotensin, though low non-spasmogenic doses in the presence of contraction by acetylcholine reduced the bradykinin relaxation. Morphine and atropine reduced the angiotensin contraction, and potentiated the bradykinin relaxation in its presence. Only atropine reduced the acetylcholine contraction and potentiated the bradykinin relaxation in its presence. Neither morphine nor atropine had any effect on the bradykinin reduction of its own responses. The magnitude of the bradykinin relaxation on the guinea-pig ileum is dependent on the manner of stimulation, rather than on the state of contraction; and, also is sensitive to regulation by agents that have their actions on the parasympathetic system. Angiotensin reduces the bradykinin relaxation by a mechanism involving its indirect parasympathomimetic effects. In contrast, the bradykinin reduction of its own relaxation is not via a parasympathetic mechanism, but probably is a direct action.