The nucleation field, by the curling mode, is calculated for an ideal chain of identical ferromagnetic spheres as a function of the angle between the applied magnetic field and the chain axis, and of the radius of the spheres, neglecting magnetocrystalline anistropy. Computations for an infinite chain using first- and second-order perturbation theory yield practically the same results so that higher order terms can certainly be neglected. Comparison with experiment will be possible only when measurements are carried out on larger radii than those experiments which have been done so far.