Jassa falcata and Corophium insidiosum are epifaunal tube-building marine amphipods, whose niches overlap in habitat and food requirements. Laboratory experiments were conducted to study the influence of the quality of different available particulate substrates on settlement and tube-building behaviour of these two amphipod species. Our experiments suggest that C. insidiosum is less specialized in this respect than J. falcata. C. insidiosum is able to use organic materials for tube-building such as artificial (Ulva spec. powder) or mixed natural detritus as well as inorganic material (coarse sand); whereas J. falcata utilizes organic materials, but sand only to a very limited extent.