In this paper we report measurements and theoretical interpretation of the lateral forces which act on YBa2Cu3Oxhigh‐Tcsuperconductors in a magnetic field and on small magnets interacting with the high‐Tcsuperconductors. The results of two types of experiments are described: In the first experiment, disk‐shaped superconductor samples are moved along the symmetry plane of a pair of Helmholtz coils, the movement being perpendicular to the magnetic field of the coils. This measurement leads to the determination of the hysteresis curves of the superconductors. A Bean‐type, critical‐state model is considered in which the high‐Tcsuperconductors are treated as an assembly of microscopic, spherical grains of uniform diameters. By taking the influence of the demagnetizing field and the Lorentz field into account, the magnetic response of the grains is derived. In the second experiment, a small magnet is laterally moved above the surface of a high‐Tcsuperconductor, the axis of the magnet being kept perpendicular to the surface. It is shown that the observed lateral force is well reproduced using the grain model if an effective value of the bulk susceptibility is incorporated. The results are presented for both the sintered and melt‐textured YBa2Cu3Ox, for the latter the effect of demagnetization being more important than for the former. Our treatment makes it possible to evaluate the lateral force using closed expressions without resorting to the numerical solution of the field equations. ©1995 American Institute of Physics.