Summary Strong pathogenic effects, including immunotoxicity and carcinogenesis of xenobiotics like TCDD and PCBs, in mammals are mainly mediated by the aryl hydrocarbon receptor (AHR). AHR-homologs have recently been shown for Caenorhabditis elegans (Nematoda), Drosophila melanogaster (Diptera) and Mya arenaria (Bivalvia). Since immune modulating effects have been described in earthworms after exposure to xenobiotics such as PCBs this investigation focused on the existence of an AHR-like molecule in Eisenia fetida. Our data revealed two proteins in tissue extracts, and one protein in coelomocyte lysates, of E. fetida that cross-reacted with an affinity purified AHR-antibody by western blot analysis. Reverse transcription of poly (A) +RNA from E. fetida and amplification of cDNA with the degenerate primers, designed for AHR detection in invertebrates as well as aquatic vertebrates, produced two independent bands of approximately 550 bp and 250bp. Efforts to identify an AHR cDNA homolog in E. fetida with RT-PCR analysis using poly (A) +RNA were not successful. Further studies using different primers and/or specific tissues and developmental stages are needed to substantiate whether or not an AHR-like molecule exists in E. fetida.