The Environmental Protection Agency (EPA), Regions 9 and 10, have developed draft guidance for implementing whole effluent toxicity (WET) programs. This guidance incorporates information on WET requirements from supporting EPA documents, such as the Technical Support Document for Water Quality-based Toxics Control (TSD, EPA/505/2-90- 001) and the EPA toxicity test method manuals, in order to provide a single concise document. A collaborative effort between Regions 9 and 10, this guidance includes input from States as well as the regulated community on some non-policy issues. This interim guidance also incorporates many comments from States, EPA headquarters, and other EPA regions. Region 9 issued the second draft of the guidance to the regulated community in Region 9 states on May 18, 1995, while Region 10 distributed the second draft on June 23, 1995. This document provides guidance to EPA permit writers and States on how best to implement EPA's National Pollutant Discharge Elimination System (NPDES) regulations regarding appropriate WET limitations and monitoring requirements in permits. It also provides guidance to the public and to the regulated community on how Regions 9 and 10 intend to exercise its discretion in implementing its regulations. This guidance is designed to implement national policy on these issues. This document does not substitute for EPA's regulations, nor is it a regulation itself.