  Superconducting transition temperature Tc of NazCo1-xMxO2.yH2O has been
studied for M=Ir and Ga, which can substitute for Co. It has been found that Tc
is suppressed by the M-atom doping. The decreasing rates |dTc/dx| are of the
order of 1 K/% and too small to be explained by the pair breaking mechanism for
the anisotropic order parameters by non-magnetic impurities. Brief arguments
are given on possible origins of the Tc suppression.
