Bacterial lipopolysaccharide (LPS) induces in 5 h a hypotensive response mediated by the B preceptor for kinins in the rabbit, an effect which is not observed in untreated animals. The present study is intended to evaluate the capacity of other acute toxic treatments to induce such a response and to analyze the mechanism of induction.Intravenous injections of inulin (20 mg), Naja venom (50 µg), compound 48/80 (1 mg), and etiocholanolone (6 mg) failed to induce hypotensive response to des-Arg9-bradykinin (the selective agonist of the B1-receptor) in 5 h. LPS from Salmonella (100 µg) and E. coli (10 µg) were highly effective, whereas trypsin (2 mg) gave doubtful responses. White blood cell counts revealed a profound and rapid neutropenic effect of the 2 LPS and a less marked one for trypsin. It is concluded that (1) LPS is a selective inducer of a new cardiovascular response to kinins mediated by the B preceptor, and (2) that the mechanism of induction may include an intimate interaction between neutrophil leukocytes and blood vessel walls.