Year-to-year variability in the ring widths of trees on flood plains along two reaches of the Potomac River near Washington, D.C., seems in large part to be related to differences in flood-flow regimes. Trees directly exposed to high flood velocities are damaged more often than sheltered trees and thus exhibit more variable ring-width patterns. The ring-width variability of unsheltered trees on low levels of flood plains is greater than that of trees on high levels, indicating that variability values are positively correlated with flood frequency. Sheltered trees, however, have less variable ring-width patterns than those of unsheltered trees, and variability is not correlated with flood frequency. As a result, ring-width variations may be used to estimate the probability of flood damage along local channel reaches of a stream. Growth responses after hydrologic catastrophies in 1948 and 1972 indicate that rings of flood-plain trees can be used to document the occurrence and crest altitude of high-magnitude floods. ?? 1982 Springer-Verlag New York Inc.