A simple method for estimating the activation sensitivity of an element/isotope, activated with cyclotron produced fast neutrons, has been developed. It uses the measured neutron spectra produced by bombarding a thick Be target with deuterons of different energies (15-54 MeV) and the measured/estimated neutron cross sections for the particular nuclear reaction. This method is applicable to all sorts of neutron spectra and all the elements/isotopes, whose cross sections/excitation functions in the relevant energy ranges, are available. We have applied this method to estimate the activation sensitivities of a number of lighter elements of biomedical interest. It is pointed out that this simple method is much cheaper, more convenient and quicker in estimating the activation sensitivities than experimental measurements - of course as long as the appropriate excitation functions are available.