One of the intriguing questions involving the copper containing high temperature superconductors is the relationship between the hole concentration and the transition temperature, Tc. We address this question in terms of a proposed “master curve” on a Tc, vs hole concentration plot. This curve shows a maximum at 90K at a hole concentration of approximately 0.2 – 0.22 holes per sheet copper for the 1–2–3 system. In this work we studied the Nd1+xBa2−xCu3Oy and YBa2Cu3−xZnxOy systems to check the validity of this “master curve”. Both Nd and Zn substitutions lower Tc, Nd by reducing the number of holes, consistent with the model given by the curve. The effect of Zn substitution is ambiguous, since both the holes are increased and the Cu-O planes are perturbed. Compensation doping, using both Nd and Zn, shows that the major effect of Zn is to disrupt the Cu-O planes.