Shear tests on undisturbed samples of clay at low normal effective stresses have proved to be useful in order to understand the actual nature of cohesion. Drammen plastic clay was considered to be a suitable material for this study as it is nonfissured and noncemented. Triaxial compression and extension tests without membranes were performed on this clay in the low stress range. The samples in compression failed along inclined planes, while those in extension failed nearly along a horizontal plane. It was found that the shear resistance in the case of extension tests was independent of the average effective normal stress in the low stress range. The magnitude of the cohesion was nearly the same as the cohesion observed in compression tests. The reasons for these differences are discussed in terms of a proposed model. The shear resistance in extension tests is probably a structural cohesion and no friction seems to be mobilized under these conditions. When the samples were reconsolidated toin situstresses, the shear parameters in extension tests were the same as in compression tests. It is, therefore, suggested that mobilization of friction depends on the nature of the contacts which undergo modification when disturbance of structure on account of reconsolidation takes place.