Purpose: Purpose of this paper is evaluation of susceptibility of high-strength structural steels to hydrogen delayed cracking. Design/methodology/approach: Susceptibility to hydrogen delayed cracking of high-strength alloy steels have been made under constant load in hydrogen generating environments. Test were carried out using round notched specimens subjected to axial tensile load being equivalence to 75-96% of maximum force obtained from a tensile tests in air. Two constructional middle carbon steel – grades 26H2MF and 34HNM were tested in used (worn out) mineral engine oil at temperature of 80°C. One low carbon weldable steel grade – 14HNMBCu was investigated in sea-water under cathodic polarization at room temperature. Presence or lack of cracking within 200 hours was chosen as a measure of susceptibility to hydrogen delayed cracking. Fracture modes of failed samples were examined with the use of scanning electron microscope. Findings: All tested steels reveal high resistance to hydrogen degradation under constant load. Hydrogen delayed cracking does not occur until the load level is as high as flow stress (yield strength). Research limitations/implications: Further research should be taken to reveal the exact mechanism of crack initiation. Practical implications: Tested steels could be safely utilized within elastic range of stress in hydrogen generating environments. Originality/value: Under the critical load and hydrogen concentration notched samples premature failed and hydrogen-enhanced localised plasticity (HELP) model is a viable degradation mechanism.