  We study the effect of radiative corrections on the structure of neutrino
mass matrix. We analyze the renormalization of the matrix from the electroweak
scale $m_Z$ to the scale $m_0$ at which the effective operator that gives
masses to neutrinos is generated. Apart from Standard Model and MSSM,
non-standard extensions of SM are considered at a scale $m_X$ intermediate
between $m_Z$ and $m_0$. We find that the dominant structure of the neutrino
mass matrix does not change. SM and MSSM corrections produce small (few
percents) independent renormalization of each matrix element. Non-standard
(flavor changing) corrections can modify strongly small (sub-dominant) matrix
elements, which are important for the low energy phenomenology. In particular,
we show that all sub-dominant elements can have purely radiative origin, being
zero at $m_0$. The set of non-zero elements at $m_0$ can be formed by (i)
diagonal elements (unit matrix); (ii) $M_{ee}$ and $M_{\mu\tau}$; (iii)$M_{ee}$
and $\mu\tau$-block elements; (iv) $\mu\tau$-block elements. In the case of
unit matrix, both atmospheric and solar mixing angles and mass squared
differences are generated radiatively.
