  To explain the origin of Herbig Ae/Be stars activity, it has been recently
proposed that strong mass-losses trigger rotational instabilities in the
envelope of fast rotating stars. The kinetic energy transferred to turbulent
motions would then be the energy source of the active phenomena observed in the
outer atmosphere of Herbig Ae/Be stars (Vigneron et al. 1990; Lignieres et al.
1996).
  In this paper, we present a one-dimensional model of angular momentum
transport which allows to estimate the degree of differential rotation induced
by mass-loss. Gradients of angular velocity are very close to - 2 \Omega / R
(\Omega being the surface rotation rate and R the stellar radius). For strong
mass-loss, this process occurs in a short time scale as compared to other
processes of angular momentum transport. Application of existing stability
criteria indicates that rotational instabilities should develop for fast
rotating star. Thus, in fast rotating stars with strong winds, shear
instabilities are expected to develop and to generate subphotospheric turbulent
motions. Albeit very simple, this model gives strong support to the assumption
made by Vigneron et al. 1990 and Lignieres et al. 1996.
