MXR transport activity was measured in living gills with Calcein-AM and quantified by computerised image analysis. Simultaneously, we detected MXR protein expression with an antibody C 219 detecting evolutionary conserved amino acid sequence of various MXR transporters. Shore crab adapted to 10%o and 33%o seawater according to the natural salinity range were studied for MXR transport activity and for protein expression in gills and digestive glands. Animals adapted to low salinities had a 30% higher transport efficiency possibly due to membrane up folding inferring that these efflux pumps maybe also involved in osmo-regulation. Animals were exposed to AAF (0.01M), a specific model inducer of the transmembrane P-glycoprotein involved in MXR transport over a period of 3 days and showed a 50% induction of transport activity in gills at both salinities. Additionally, animals were starved for 4 weeks, re-fed once, and samples taken after 4, 8, 12, 24 and 48 hours according to cell differentiation of the digestive gland. In the digestive glands MXR proteins appeared in differentiating blister cells 8 hours after re-feeding as immuno-localised with the AB C219. Simultaneously, food supply induced a complete breakdown of MXR transport activity in gills after 8 h. MXR-like transporters, presumably P-gp, appear to exist in shore crab as transport can be specifically induced by a model inducer. Furthermore, gills and hepatopancreas appear to perform a sort of physiological job sharing in which hepatopancreas overtakes xenobiotic elimination during periods when gills are involved to serve enhanced oxygen demands during digestion and active ammonia excretion.