Lemna gibba (a duckweed) is a freshwater macrophyte commonly used in toxicity testing, and Lemna spp are currently the only aquatic higher plants required for evaluation of pesticides under the pesticide registration guidelines of the EPA. The methods currently available for toxicity testing by various organizations and agencies, including ASTM, OECD, EPA and Environment Canada, are largely static or semistatic tests with unspecified renewal intervals (OECD) and may not provide a consistent means of exposure owing to short toxicant half-life in aquatic media, uptake of chemical by plants and evaporation of nutrient media. The procedure outlined here details a simple and efficient 7-day daily static renewal procedure for conducting toxicity tests with L. gibba, the appropriate end points to assess, the statistical criteria necessary for analyzing the toxicity data, as well as the steps required to culture and maintain L. gibba. This protocol is based on a modified version of a widely accepted static method.