  We study the wellposedness of Cauchy problem for the fourth order nonlinear
Schr\"odinger equations i\partial_t u=-\eps\Delta u+\Delta^2
u+P((\partial_x^\alpha u)_{\abs{\alpha}\ls 2}, (\partial_x^\alpha
\bar{u})_{\abs{\alpha}\ls 2}),\quad t\in \Real, x\in\Real^n, where
$\eps\in\{-1,0,1\}$, $n\gs 2$ denotes the spatial dimension and $P(\cdot)$ is a
polynomial excluding constant and linear terms.
