The vibrational characteristics of a slant-cracked rotor passing through its flexural critical speed have been analysed by using finite element method for flexural vibrations. The transient response of a cracked rotor has been obtained by applying an unbalance force and a harmonically varying torque on it. When a crack is present in the rotor, the sub and super harmonic frequency components at an interval frequency corresponding to torsional frequency were found to be centered on critical speed of the rotor system. A parametric study has been carried out for transient response of the rotor for different crack depths, rotor angular accelerations and torsional frequencies. Some suggestions for detection and monitoring of the slant cracks in the rotor are described. © 2002 Published by Elsevier Science Ltd.