The report describes the interlaboratory method study that was performed to evaluate interim Method 450.1 for total organic halides (TOX). In the method, a measured volume of water is passed through two columns in series each containing 40 mg of activated charcoal. Organic halides (OX) present in the water are adsorbed onto the charcoal which is washed to eliminate trapped inorganic halides. The contents of the columns are then pyrolzed converting the halides to titratable species that are measured microcoulometrically. In this study, three water matrices, reagent water, ground water, and surface water were spiked at six concentrations with a solution containing a combination of four model compounds. These were lindane, bromoform, pentachlorophenol, and tetrachloroethene. A chlorinated drinking water diluted to four concentrations with distilled water were also analyzed. Ten laboratories participated in the study. Data obtained were analyzed using a standardized package known as Interlaboratory Method Validation Study (IMVS), which is designed to implement the recommendations of ASTM Standard D-2777. The IMVS package includes rejection of outliers; estimation of mean recovery as a measure of bias; estimation of single-analyst and overall precision, and tests for effects of water type on these parameters.