The Data Reporting Guideline (DRG) for Photolysis Studies in Water and on Soil, Series 161-2 and 161-3, 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 the light source and relationship to natural sunlight, characteristics of the soil or water used, the equipment, experimental design, analytical method, description of the handling and analysis of samples 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 161-2 and 161-3, Photolysis Studies in Water and on Soil 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.