  High-Sensitivity Electron Paramagnetic Resonance experiments have been
carried out in fresh and stressed Mn12-Acetate single crystals for frequencies
ranging from 40 GHz up to 110 GHz. The high number of crystal dislocations
formed in the stressing process introduces a E(S_x^2-S_y^2) transverse
anisotropy term in the spin hamiltonian. From the behaviour of the resonant
absorptions on the applied transverse magnetic field we have obtained an
average value for E = 22 mK, corresponding to a concentration of dislocations
per unit cell of c = 10^-3.
