This report documents findings related to sources of microorganisms available for removal by urban runoff in well-defined residential drainage areas in Baltimore City, over an 8 month period. High densities of indicator microorganisms were found in urban sites that had high population densities and were generally in poor sanitary condition, as compared to a site that had a low population density and was well-maintained. It is highly probable that the microbial quality of runoff from 'dirty' sites would improve significantly if more attention were paid to upgrading sanitation and stricter enforcement of litter laws in these areas.