Methoxychlor (2,2-bis(methoxyphenyl)-1,1,1-trichloroethane) and DDT (2,2-bis(chlorophenyl)-1,1,1-trichloroethane) undergo different hydrolytic degradation pathways in water at pH's common to the aquatic environment. For methoxychlor at common aquatic pH's, the reaction is pH independent, and at 27 degrees the half-life is about 1 year. On the other hand, for DDT the reaction is pH dependent, and at 27 degrees and pH 7 the half-life is about 8 years. The major products of methoxychlor hydrolysis at pH 7 are anisoin, anisil, and DMDE (2,2-bis(methoxyphenyl)-1,1-dichloroethylene); the major product of DDT is DDE (2,2-bis-(chlorophenyl)-1,1-dichloroethylene). Hydrolytic degradation half-lives of metabolites and reported breakdown products are estimated and compared with the parent compounds. The contribution of hydrolysis is dependent on the amount of methoxychlor and DDT in aqueous solution. Calculations with partition coefficients indicate that even though high concentrations of these two compounds are present in the sediment and biota, a large fraction can be in solution.