An estimated 52,500 birds died as a result of 7 major oil spills on 2 mid-Atlantic estuaries between 1973-78. Ruddy ducks (Oxyura jamaicensis) constituted 98% of 12,500 birds known to have died from 5 spills on the Delaware River. Seventy-six percent of 40,000 dead birds from 2 Chesapeake Bay spills were horned grebes (Podiceps auritus) and oldsquaw (Clangula hyemalis). Oiled waterfowl that were captured alive (6% of the estimated mortality) were cleaned with a variety of cleaning agents and techniques. High mortality occurred during and shortly after cleaning, and was apparently due to hypothermia and to toxicity of solvent cleaning agents. Eighty-two percent of the 3,113 birds that were cleaned died prior to or at time of release. The fate of the remaining 18% is unknown. Petroleum solvents used as cleaning agents were toxic to the birds. Most detergents left a surfactant (wetting agent) on the feathers which resulted in subsequent wetting of released birds. Although rehabilitation techniques have improved in recent years, high bird mortality can be expected following future oil spills.