The design of complex products such as automobiles and aircraft often requires performing repeated dynamic analyses using detailed finite element models. The high computational costs and long turnaround times associated with the use of these models can impede the design process.In this paper, a practical method for performing efficient design parameter studies using Eigensolution Reanalysis is discussed. Special purpose software has been developed which interfaces with commercial finite element analysis codes. The special purpose software uses the baseline modes to calculate new modes for each design change. The software can also compute forced response of the modified designs given user specified dynamic load cases.This method provides dramatic savings in CPU time compared to the traditional method of re-solving the full eigenproblem for the modified design modes. Typically, the reanalysis calculations use less than five percent of the CPU time required for the baseline analysis. This means that the design parameter study may now become an interactive activity, thus reducing the required engineering time significantly.