  Non-local conserved charges in two-dimensional sigma models with target
spaces $SO(2n)/SO(n){\times}SO(n)$ and $Sp(2n)/Sp(n){\times}Sp(n)$ are shown to
survive quantization, unspoiled by anomalies; these theories are therefore
integrable at the quantum level. Local, higher-spin, conserved charges are also
shown to survive quantization in the $SO(2n)/SO(n){\times}SO(n)$ models.
