  We study $np\to \Lambda\Theta^{+}$ and $np\to \Sigma^{0}\Theta^{+}$ processes
for both of the positive and negative parities of the $\Theta^{+}$. Employing
the effective chiral Lagrangians for the $KNY$ and $K^*NY$ interactions, we
calculate differential cross sections as well as total cross sections for the
$np\to \Sigma^0 \Theta^+$ and $np\to \Lambda\Theta^+$ reactions. The total
cross sections for the positive-parity $\Theta^+$ turn out to be approximately
ten times larger than those for the negative parity $\Theta^+$ in the range of
the CM energy $\sqrt{s}_{\rm th}\le \sqrt{s}\le 3.5 {\rm GeV}$. The results are
rather sensitive to the mechanism of $K$ exchanges in the $t$ -- channel.
