In order to determine the potential of pesticides to cause damage to nontarget terrestrial plants, assessments of the intrinsic toxicity of the pesticide must be matched to estimates or measures of exposure. This paper describes a glasshouse bioassay which has been developed in order to assess pre- and postemergence toxicity of pesticides to a taxonomic range of crop and weed species. Different techniques used to assess pesticide effects in these tests are compared, and their contribution to the overall toxicological hazard assessment is shown. Use of the glasshouse bioassay to compare (a) effects of a given herbicide on different plant species, (b) effects of different herbicides on one plant species, and (c) differences in pre- and postemergence effects for a given herbicide are demonstrated. Interpretation of the ecological risks in the field based on the glasshouse toxicity data is discussed.