Five laboratory studies of benthic macroinvertebrate recolonization were conducted for six-wk periods to evaluate the effects of physical scaling factors (i.e., microcosm size, seawater flow rates and sediment depth) on benthic community structure. Design variables included four open-faced acrylic containers of size 7, 12, 20 and 32 cm sq; seawater flow rate - approximately 0.7 or 1.6 liters/min; and sediment depth of 2.5 or 5.0 cm. Effects of seawater flow rates were more apparent than those related to microcosm size and sediment depth. The various indices usually did not vary significantly with physical scaling factors. These results provide a basis for setting minimum experimental unit parameters and should lead to cost savings through physical scale reduction (depth of sediment and surface area) and less time to process smaller volumes of sediment and generation of smaller waste volumes.