Mechanisms of the variability of the line profiles in spectra of OB stars have been investigated. The main cause of appearance of the Discrete Absorption Components in the absorption parts of the resonance line profiles was supposed to be a motion of dense clumps in the atmosphere. The variable profiles of UV resonance doublets of CIV and SiIV in the spectra of OB stars are calculated in the framework of the stochastic clumping model of the wind.