The rotordynamic response of an imbalanced rotor accelerating through its first lateral bending critical speed was investigated both analytically and experimentally. A two degree-of-freedom lumped mass, damping and stiffness model was developed to simulate the response of a simply supported, single disk rotor during both acceleration and deceleration. The equations of motion were then solved numerically. The computer model was used to determine the effect of acceleration rate, asymmetric stiffness and damping, and acceleration scheduling on the maximum amplitude of the response. Experimental data for a simply supported, single disk rotor accelerating at different rates were compared with the computer model. Increased acceleration rates and damping reduce the magnitude of the response. Asymmetric stiffness and acceleration scheduling can also be used advantageously to reduce the maximum amplitude of the response.