At the request of Environmental Protection Agency (EPA) project coordinators, two special quality assurance components were included in a study of herbicides in rural wells in Iowa. Since the study involved daily sampling of 88 rural wells for a period of four to five weeks, it was anticipated that samples would be in refrigerated storage for up to eight weeks during which microbial and chemical activity could lead to analyte loss. The sample degradation study reported here was conducted to insure that water samples containing three herbicides (atrazine, alachlor, and metolachlor) did not undergo excessive losses during storage. Results indicate no reduction in pesticide concentrations in six refrigerated water samples analyzed weekly during an eight-week storage period.