The Data Reporting Guideline (DRG) for Hydrolysis Studies, Series 161-1, gives guidance to pesticide registrants on the format for their study report so that the Agency can review it efficiently. The guidance clarifies sections in the existing Pesticides Assessment Guidelines, Subdivision N, on data reporting. It provides an outline for the study report and describes the topics which should be addressed such as sampling intervals, source or preparation of buffers, the equipment used, method of sterilization, pH monitoring, description of the handling and analysis of samples, etc. and provides guidance on the presentation of the results of the study. Data submitters can use the DRG in preparing their reports for submission to EPA to meet 40 CFR 158 requirements for the registration of pesticides. The DRG for Series 161-1, Hydrolysis Studies is only one of a number of DRG's published by the National Technical Information Service as an addendum to Subdivision N of the Pesticide Assessment Guidelines.