The eigenmode equation governing both the toroidicity-induced and the ion-temperature-gradient-driven modes of arbitrary wavelengths in tokamaks is derived by employing the ballooning-mode formalism. For the toroidicity-induced mode (electron driftwave), the ion magnetic drift resonances are de-stabilizing and can have a significant effect when the temperature ratio, Te/Ti, is of order unity. The ion-temperature-gradient-driven mode (ion drift wave), which is unstable in a sheared slab geometry, is found to be further de-stabilized by the ion magnetic drifts, resulting in a lower critical ion temperature gradient (ηi).