Finding the history of a groundwater contaminant plume from measurements of its current spatial distribution is an ill-posed problem and, consequently, its solution is extremely sensitive to errors in the input data. In this paper, Tikhonov regularization (Tikhonov and Arsenin, 1977) is used in numerical experiments to recover the release history of a plume that has originated from a known, single site. The recovered release history is then used to reconstruct the plume evolution history. The method is found to be insensitive to round off errors, but its accuracy is affected by plume measurement errors, the extent to which the plume has dissipated, and, to a lesser degree, the accuracy of the transport parameter estimates. A regularization approach may be effective at finding a plume history when there are adequate data. ¿ American Geophysical Union 1993