Cyclic loading and large deformations may significantly reduce the undrained shear strength of clay. The stability of constructions and clay slopes can be significantly affected if subjected to disturbances from large local loads and different kinds of construction works such as piling, blasting, etc. The risk for widespread failures may be particularly high when quick clay is present in the area. At the Swedish Geotechnical Institute, a study has been performed on the susceptibility to disturbance from cyclic stresses and strains of different clays. The influence of different factors on the strength degradation has been examined in series of laboratory tests on different types of sensitive clays. The laboratory tests on the soils have included basic characterisation tests, CRS oedometer tests and active static and cyclic triaxial tests. The triaxial tests have been performed at various overconsolidation ratios with varying cyclic shear stress levels and deformation levels. In the field, trials with cyclic T-bar tests in situ have also been performed. The results of the study have given an increased insight into the effect of cyclic stresses and deformations on the degradation of different types of clay.