Phospholipases A(2) (PLA(2)s) are enzymes that cause the liberation of fatty acids and lysophospholipids by the hydrolysis of membrane phospholipids. In addition to their catalytic action, a wide variety of pharmacological activities have been described for snake-venom PLA(2)s. BmooPLA(2)-I is an acidic, nontoxic and catalytic PLA(2) isolated from Bothrops moojeni snake venom which exhibits an inhibitory effect on platelet aggregation, an immediate decrease in blood pressure, inducing oedema at a low concentration, and an effective bactericidal effect. BmooPLA(2)-I has been crystallized and X-ray diffraction data have been collected to 1.6 Å resolution using a synchrotron-radiation source. The crystals belonged to space group C222(1), with unit-cell parameters a = 39.7, b = 53.2, c = 89.2 Å. The molecular-replacement solution of BmooPLA(2)-I indicated a monomeric conformation, which is in agreement with nondenaturing electrophoresis and dynamic light-scattering experiments. A comparative study of this enzyme with the acidic PLA(2) from B. jararacussu (BthA-I) and other toxic and nontoxic PLA(2)s may provide important insights into the functional aspects of this class of proteins.