Brucella abortus releases two components (fractions 3b and 10) that inhibit the myeloperoxidase- H202-halide antibacterial system of bovine neutrophils by inhibiting degranulation. Fractions 3b and 10 were analyzed by high-performance liquid chromatography and thin-layer chromotography and compared with nucleotide and base standards. These investigations indicated that fraction 3b coeluted and co migrated with 5' -guanosine monophosphate (GMP), whereas fraction 10 coeluted and comigrated with adenine. We determined the biologic effects of GMP, adenine, and B. abortus fractions 3b and 10 on neutrophil functions. Iodination activity of neutrophils was inhibited to rv6507o of control by GMP (0.04 mg/ml) and by fraction 3b (0.04 mg/ml). Iodination was also suppressed to rvSO% of control by adenine (0.04 mg/ml) and by fraction 10 (0.04 mg/ml). These results suggest that B. abortus produces GMP and adenine and that these substances contribute to the intracellular survival of the bacteria.