  We discuss conditions for the integrability of an almost complex structure
defined on the total space of an induced Hopf S^3-bundle over a Sasakian
manifold . As an application, we obtain an uncountable family of inequivalent
complex structures on the Stiefel manifolds of orthonormal 2-frames in C^{n+1},
non compatible with its standard hypercomplex structure. Similar families of
complex structures are constructed on the Stiefel manifold of oriented
orthonormal 4-frames in R^{n+1}, as well as on some special Stiefel manifolds
related to the groups G_2 and Spin(7).
