The results of research into the relation between rainfall and run-off from small urban areas in St. Louis, Mo., are here presented as specific studies of the run-of/ from parts of two different city blocks tributary to street inlets and from both roofs and ground surface of another entire city block. The information submitted results from measurements of rainfall and storm flow for practically all heavy rains occurring from 1914 to 1933. The ratio of run-off to rainfall, defined in several ways, is shown to vary over a wide range. Rainfall rates at each of the locations studied are reduced and developed into frequency diagrams, and these three rainfall studies, with one other, are combined into a master frequency study for the general region. Runoff is also studied as an independent phenomenon; the run-off frequency curves are developed in a form similar to the rainfall diagrams. The two sets of curves are considered to be comparable as representing equivalent probabilities of occurrence. Ratios are then developed between corresponding values. Within certain limits, it is suggested that these ratios may be applied to proper rainfall frequency curves for other localities and will give approximate run-off values for similar conditions of surface. Suggestions are offered as to how the values determined for specific blocks in St. Louis might be modified further to be applicable to (a) different surface slopes; (b) other percentages of impervious area; and (c) other typical soils. For Class (c), adaptation factors are determined by sprinkling, at definite rates, a number of segregated areas of bare soil and of turf.