Magnetic structures and magnetization processes in arrays of closely packed Ni nanowires (length l=1 μm, diameter d=40 nm, and period: 100 nm) are investigated by means of micromagnetic modelling. The simulations are performed with an algorithm based on the finite element method combined with the boundary element method which allows for the accurate calculation of magnetostatic interactions. Magnetization states of Ni nanowires at zero field are calculated. Only few, simple magnetization configurations result to be stable. Transient states of the magnetization indicate that magnetization reversal occurs by means of nucleation at the ends of the particles and subsequent soliton propagation. Hysteresis loops of up to 16 interacting nanowires are simulated. It turns out that magnetostatic interactions between the wires have a significant influence on the switching field. © 2001 American Institute of Physics.