The Speedvale Experimental Basin, a 210 ha watershed on the outskirts of Guelph, Ontario, was established in 1965 as an International Hydrological Decade project for the purpose of studying impacts of urbanization on hydrologic response. A relatively extensive hydrologic database regarding precipitation, streamflow, soil moisture, and groundwater has been assembled for the preurbanization period from 1966 to 1974 and for the period of ongoing development from 1975 to 1982. The study area, located physiographically within the Guelph Drumlin Field, was used for mixed agricultural purposes prior to 1974. During 1975 and 1976, 155 ha of the basin were serviced for development for light industrial and commercial usage, dramatically altering the configuration of the drainage system. The major alteration was the installation of a stormwater conveyance system, consisting of a large-diameter storm sewer (2.5 and 3.0 m) and a network of open drainage ditches outletting through ditch inlet catch basins into a main drainage channel.With the changes in land use in the basin have come changes in both volumetric and time distribution aspects of hydrologic response. Changes in the response include (i) an increase in the mean annual runoff coefficient by a factor of 1.5, (ii) an increase in the average annual maximum instantaneous discharge by a factor of almost 3.0, (iii) a change in the time of the annual peak flow from occurring solely in the spring runoff period to occurring throughout the various seasons, (iv) a change in the seasonal pattern of monthly runoff coefficients, with the greatest change observed in the summer and lesser changes observed in the other seasons, (v) a 3-fold reduction in unit hydrograph lag time, and (vi) a 3.5-fold increase in unit hydrograph peak discharge. Key words: urbanization, hydrology, surface water runoff, streamflow, watersheds.