Aim. To perform full assignment of IR spectra of steroid hormones, testosterone and ethyniltestosterone and to connect vibrational frequency and intensity of IR absorption bands with the peculiarities of electronic structure and geometry of the above hormones. Methods. Calculations of vibrational frequency and intensity of IR bands of testosterone and ethyniltestosterone are performed using the density functional theory within the B3LYP/6-31G** approach with a complete geometry optimization by the gradient method. Results. Complete assignment of IR absorption bands of testosterone and ethyniltestosterone is performed. Conclusions. For the first time the frequencies and normal modes of vibrations are predicted in the low-frequency region of the IR spectrum. Biological importance of the obtained results is discussed