1. The modulation of the spontaneous increase in contractile responses to des-Arg9-bradykinin (des-Arg9-BK) of rabbit aortic strips incubated in vitro was studied. Rapid hypotensive responses to exogenous kinins were also measured in rabbits anaesthetized 5 h following pretreatment. 2. Continuous exposure to the protein synthesis inhibitors cycloheximide (71 microM) or anisomycin (3.8 microM) profoundly inhibited the sensitization to des-Arg9-BK in incubated aortic strips. However, temporary (3 h) inhibition of protein synthesis in vitro followed by further incubation (3 h) of tissues without inhibitor, paradoxically enhanced both the maximal contractile responses to des-Arg9-BK (1.7 microM) and the apparent affinity of the kinin without affecting contractions to noradrenaline (NA, 100 nM) at 6.5 h. 3. The stimulatory activity of the short treatment (pulse) with cycloheximide was abolished in the presence of dexamethasone sodium phosphate (100 microM throughout the incubation). The function of receptors for kinins did not appear to be altered directly by the steroid treatment. 4. Interleukin-1 beta (IL-1 beta), applied at low concentrations (100-250 pg ml-1) on aortic strips between 3 h and 6.5 h of incubation time, mimicked the selective stimulatory effect of the cycloheximide pulse on responses to des-Arg9-BK. Higher concentrations of IL-1 beta (0.5-5 ng ml-1) did not further amplify the responses to des-Arg9-BK but decreased the contractile responses to NA. 5. The modulation by IL-1 beta of vascular sensitivity to des-Arg9-BK and to NA was prevented by blockade of protein synthesis. 6. The induction in vivo by IL-1 beta (5 micrograms kg-1) or by cycloheximide (10 mg kg-1) of cardiovascular responsiveness to des-Arg9-BK was demonstrated with a blood pressure assay of exogenous kinins or with tissues isolated ex vivo 5 h after pretreatment of animals. Evidence of active disposition of cycloheximide in vivo was also obtained. 7. We propose the production of endogenous IL-1 as a possible mechanism for the enhancement of responsiveness to des-Arg9-BK observed in tissues pulsed with a protein synthesis inhibitor and for the inducing effect of cycloheximide or E. coli lipopolysaccharide in vivo. These results suggest that effects mediated by the BK1 receptor for kinins are potentially present in pathological conditions associated with IL-1 production.