A reverse phase HPLC method for the quantitative determinations of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and its degradation products in alginate-based alachlor controlled release formulations has been developed. Sonication and the addition of sodium ethylenediaminetetraacetate as a chelating agent were employed to disintegrate the formulation matrix. The disintegrated formulations were extracted with acetonitrile. The acetonitrile extracts were analyzed for alachlor and its degradation products by HPLC. A C18column with a mobile phase of 65% acetonitrile and 35% water was used for separation. A UV detector set at 215 nm was selected for quantitation, and a photodiode array detector was used for confirmation. The developed method was used for the determinations of the percent active ingredient in freshly prepared and aged alachlor formulations made with and without oil (linseed, soybean, or corn oil). The method was also applied to monitor the rate of release and the fate of alachlor in controlled-release studies of alachlor formulations in water. Alachlor degradation products, N-demethoxymethylalachlor and 2,6-diethylaniline (trace), were found in the formulations with oil but not in formulations without oil. The degradation of alachlor continued slowly as the formulations aged.