Creep of a neck between two rigid spherical particles of the same size by coupled grain-boundary and surface diffusion has been simulated. Both tension and compression are considered. In general, the calculations confirm that the rates of particle approach and neck growth under loading are linear functions of the level of loading. The linearity holds even during non-equilibrium regimes of deformation when curvature of the particle surfaces in the neck area depends on the external loading. Special attention was devoted to the exceptions from the linear behaviour. As a first example of non-linear behaviour, creep under tensile loading is considered. It is shown that tensile loading can lead to the formation of crack-like cavities in the neck between particles. The crack growth rate is a non-linear function of the level of external loading. Initially, it was assumed that loss of pore stability under high compressive loading could also lead to a non-linear creep regime. However, the calculations do not reveal unstable collapse of pores. For the lower levels of stress of the order of the sintering stress, non-linear behaviour is detected both for tension and compression at the moment of transition from one stage of pressure-assisted sintering to another. Despite their transient nature, nonlinear regimes play an important role in creep because they connect together different stages of linear behaviour. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.