Supersymmetric Box Contributions to $e^{+}{e}^{-}\to Z^0{h}^0$ and $e^{+}{e}^{-}\to A^0{h}^0$

Within the MSSM we calculate the electroweak 1-loop box contributions to the processes $e^{+}{e}^{-}\to Z^0{h}^0$ and $e^{+}{e}^{-}\to A^0{h}^0$. We present detailed results for c. m. energies $\sqrt{s}=200$ GeV and $\sqrt{s}=500$ GeV as well as for $\tan \beta =2$ and $\tan \beta =50$. The box contributions to the process $e^{+}{e}^{-}\to Z^0{h}^0$ are, depending on $\sqrt{s}$ and $\tan \beta$, of the order -2 to -20% and to $ e^+ e^- \rightarrow A^0 h^0 $ of 2 to 10%.