The paper presents results regarding cooling intensities of quenching oil of domestic production and of polymeric water solutions. Numerous residual stresses measurements on heat-treatment steel specimens with different masses were made. To measure the residual stresses, the relaxation method was used, involving gradual mechanical removal of the hardened layer in which the deformation of the specimen was measured by resistance strain gauges. On the basis of the measured strain at a specific depth of material removal, it is possible to calculate the size or variation of residual stresses depending on the depth of the hardened layer. Numerous residual stresses measurements provided very important data on various steels when using different quenching agents.