Bordetella pertussis produces a number of virulence determinants which contribute to its pathogenicity. One factor, the adenylate cyclase toxin (ACT), has been suggested to directly penetrate human phagocytes and disrupt their normal function by direct production of intracellular cyclic AMP (cAMP). Experiments evaluating the production of cell-associated ACT in liquid cultures of B. pertussis 504 demonstrated that the greatest activity was observed during mid-log-phase growth. Urea extracts of cells harvested during the time of maximal ACT production have been used to purify the toxin with both biological and enzymatic activities. ACT is a protein with an apparent molecular mass of 220 kDa and an isoelectric point of 7.0. The specific activity of purified ACT is 17,000 mumol of cAMP formed per mg per min. The the biological specific activity of purified ACT is 6,250 nmol of intracellular cAMP formed per mg per min in 2 x 10(6) S49 lymphoma cells per ml. Preparations containing 8 micrograms of ACT completely abrogated the chemiluminescence response of 2 x 10(6) human neutrophils per ml.