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A 3-year study (2001-2003) was conducted to determine possible unintended effects of Bt-maize (Mon810, cultivar Novelis) cultivation on nontarget organisms of the arthropod community compared with an isogenic maize line (cultivar Nobilis) with and without an insecticide treatment. Furthermore, suitable monitoring organisms and appropriate methods are recommended for Post Market Environmental Monitoring. The experimental site was situated near Bonn (Germany) and consisted of two maize fields divided into 24 plots (8 per treatment). Maintenance of the field was as customary at this site. Five different methods were adopted (samples of maize cobs, sweep net catching, visual assessments, coloured traps and jarring samples of maize panicles) in order to measure the abundance of a wide ecological spectrum of non-target herb layer arthropods. Additionally a monitoring especially aligned on cicadas as possible monitoring organisms was performed. Seven statistically significant differences in nontarget-arthropod abundance between Bt-maize and the isogenic control concerning one predator and four different herbivores were observed in this study. At single sampling dates spiders, thrips and the beetle Cortinicara gibbosa were found in significantly higher abundances in Bt maize than in the isogenic control. In 2002, at two sampling dates, cicadas were more abundant in Bt maize than in the isogenic control. A significantly lower abundance in Bt maize compared to the isogenic control was found at single sampling dates for the aphid Sitobion avenae and thrips. The results of this study indicate no biological relevant effect of the Bt maize cultivar Mon810 on nontarget arthropods compared to conventional maize. 90 statistically significant differences in arthropod abundance, caused by the application of chemical insecticide, were detected with different methods. 46 times the abundance of an arthropod taxon was significantly different in the insecticide treated plots and in Bt maize, 44 times the abundance was significantly different in the insecticide treated plots than and in the isogenic control. A significantly lower abundance of herbivorous cicadas and thrips in the insecticide treated plots than in Bt maize and the isogenic control, could be detected in several years with different methods. The same was observed for predatory arthropods like bugs, lacewings and spiders. Compared to that, aphids were significantly more abundant in the insecticide treated plots than in both other treatments, which could be detected in several years with different methods. Suitable herbivore arthropods for a monitoring of nontarget arthropod abundance in maize could be the cicada species Zyginidia scutellaris and the thrips species Limothrips cerealium and Frankliniella tenuicornis. On the next trophic level bugs of the genus Orius sp. could be used as indicator organisms. Adults of Orius sp. are polyphagous. The combination of these arthropods provide direct or indirect exposure to the metabolic products of maize plants, a high consistency of appearance all over Europe and sufficient abundances in maize fields for an appropriate statistical analysis of the data. Three methods were found to be suitable for detecting changes in the abundance of the possible indicator arthropods (L. cerealium, F. tenuicornis, Zyginidia scutellaris, Orius sp.). Standardized sweep net catching is most suitable for the collection of the cicada Zyginidia scutellaris. Standardized sampling of maize cobs as well as jarring samples of maize panicles is suitable for collecting thrips and bugs (particularly Orius sp.). All methods can be standardized and enable to sample a comprehensive arthropod community from the field, so that potential effects in biodiversity on different trophic levels can be detected and evaluated. Additionally each of these methods combines capturing individuals in sufficient numbers and cost-effectiveness. According to the results of this study, the cultivation of the transgenic maize cultivar Mon810 is a promising alternative to a conventional maize cultivation with application of chemical insecticide in infestation areas of the European corn borer (ECB) having no reproducible negative impacts on the nontarget arthropod fauna.