A new stabilization approach for linear plants with input delay and an unknown harmonic disturbance affecting the input and the output is presented. To solve this problem, the well-known predictor feedback approach with a state observer and an adaptive scheme, identifying the frequency of the disturbance, is combined. Compared to the existing approaches, the structure of our adaptive scheme is simpler. The proposed approach is applicable to plants of arbitrary relative degree, that may be unstable and non-minimum phase.