  What do we know about CPT symmetry? We conclude that the direcrt measurement
of CPT violation leads to a result that CPT violation force is limited to about
30% of CP violating forces. The best test of CPT symmetry is to see if
theoretical prediction for the phase of eta_{+-} and eta_{00} agree with
experiments. We discuss uncertainties associated with this prediction, and how
to improve it. A new test of CPT is also discussed.
