L-Amino-acid oxidase from the venom of Vipera ammodytes ammodytes, the most venomous snake in Europe, was isolated and crystallized using the sitting-drop vapour-diffusion method. The solution conditions under which the protein sample was monodisperse were optimized using dynamic light scattering prior to crystallization. The crystals belonged to space group C2, with unit-cell parameters a = 198.37, b = 96.38, c = 109.11 A, beta = 92.56 degrees . Initial diffraction data were collected to 2.6 A resolution. The calculated Matthews coefficient is approximately 2.6 A(3) Da(-1) assuming the presence of four molecules in the asymmetric unit.