The modes on how these pesticides affect non-target species are even less known and to understand its risks still constitutes a challenge. Dimethoate is one of the most used insecticides in agricultural fields and it is known as a cholinesterase inhibitor acting at the cholinergic synapses of insects. This ability to inhibit cholinesterases has been demonstrated for other groups of organisms like freshwater shrimps, chironomids, fish or earthworms. Besides these effects related to its mode of action in insects, dimethoate have been described to inhibit steroidogenesis in rats. Atrazine is an herbicide, also widely applied, which has the function of inhibiting photosynthesis in photosystem II of plants. In frogs, fish and rats, atrazine has been described as a possible endocrine disruptor and as an immunotoxin. Salvianolic-acid-B carbendazim is the predominant metabolite of the systemic broad spectrum Apoptosis Activator 2 fungicide benomyl, known for affecting the nucleus division by inhibiting microtubule assembly in fungi. The antimitotic action of carbendazim has also been described for mammals. Toxicity mechanisms of these three pesticides on invertebrates, and in particular on soil invertebrates, are by far less known. Enchytraeus albidus are an ecologically relevant invertebrate species and present in soils worldwide. They play a key role in the functioning of the soil ecosystem, being involved in the degradation of organic matter and improving the pore structure of the soil. These organisms are often used as test species for soil toxicity testing and studies have reported effects of dimethoate, atrazine and carbendazim on its survival, reproduction and avoidance behaviour. The mechanisms of such toxicity are still to be understood. The development of a cDNA microarray for E. albidus provided a new tool to assess molecular mechanisms of pesticide toxicity. This microarray was enhanced with the development of two new cDNA libraries enriched with metal and pesticide responsive genes, and all the sequence information was made available. The main goal of the present study was to investigate the early transcription responses of E. albidus to three pesticides with different modes of action: dimethoate, atrazine and carbendazim. Ultimately, the objective is also to identify key biological processes affected that indicate mechanisms of toxic action for each pesticide. Gene expression studies of pesticides in invertebrates are still scarce and, to the authors�� knowledge, this is the first transcriptomic study of dimethoate and carbendazim effects in invertebrates. Transcription effects of atrazine have been assessed in a few studies. In order to further understand the underlying transcription responses for effects at higher levels of biological organization, organisms were exposed for 2 days to a range of concentrations with known effects on reproduction in the number of juveniles, respectively. The total number of over and under expressed transcripts in each of the pesticide conditions is represented in Figure 1. In general, higher concentrations of the tested pesticides affected more transcripts than lower ones. Atrazine affected the lowest number of transcripts in total. In exposure to carbendazim it was possible to observe dose-response relation, increasing the number of differentially expressed genes with increasing concentrations. There was also a tendency for higher up-regulation with increasing concentrations.