Although our understanding of many renal mechanisms has been advancing rapidly over the past few years, there is still a dearth of information about changes that occur in renal function during pregnancy — surely one of the greatest physiological disturbances possible. It is difficult in many instances to find a description of the changes that occur quite apart from the underlying alterations in mechanisms that are responsible for them. Part of the difficulty has arisen because of the ethical and methodological problems that arise when women are used as ‘experimental animals’ until recently there has not been a suitably documented animal model, though whether this was because of technical difficulties or lack of interest on the part of investigators is not known. Recently, however, it has become apparent that many changes in renal function in the rat are similar to those occurring in women and some aspects of renal function in the rat have been investigated in detail. Since not all aspects of renal function can be covered in this review we shall concentrate on three of the more important areas, namely haemodynamics, sodium and water handling and glucose excretion, and discuss how these are changed during pregnancy; comments on the possible mechanisms involved in these changes are presented where appropriate.