The colonization of limestone bricks and bitumen coated limestone bricks by benthic river organisms was followed over time. After nine weeks of colonization, no massive increase in the numbers of bacteria on the bitumen was noted, suggesting that degradation was not proceeding rapidly. However, subjective changes in the character of the bitumen did take place, indicating that some form of degradation was proceeding. Of the other components examined, only chlorophyll a concentrations were radically different on the bitumen and this may have been due to an interference by the bitumen in the analysis. The carbohydrate concentrations, micro-invertebrate numbers and biomass, and macroinvertebrate numbers were generally similar on bitumen coated and control bricks, suggesting that bitumen or oil sand is not radically different from limestone as a substrate for benthic river communities per unit of surface area. A second study followed the response of the microbial and macro-invertebrate community on limestone bricks to the addition of synthetic crude oil (SCO). Out of the 20 taxonomic groups examined and four biochemical parameters, only one of these; the Cyanophyta, showed any apparent response to the oil addition. Thus, based upon the mode of presentation of the oil to the community, it would appear that SCO has only a minimal effect, possibly due to limited penetration. The significance of these findings to more prolonged spills is discussed with relation to the observed stimulations of benthic communities growing on oil soaked substrates. It is suggested that the interplay of the penetration of oil to the communities and its subsequent effects be investigated further.