Studies have been made of the relationship between the rainout of radioactivity in convective storms and three rainfall factors: rainfall volume, storm duration, and rainfall rate. Data were used from four densely gaged sampling networks operated during the spring and summer of 1962–1964 in central Illinois. The network areas ranged from 10 to 6000 mi2and provided data on both microscale and mesoscale relationships. Analyses of spatial variability showed a trend for the relative variability of radioactive rainout to (1) exceed the storm rainfall variability, (2) decrease with increasing rainfall volume and storm duration, and (3) increase with increasing network size. Investigation of the point representativeness of single measurements of radioactive rainout in a 15‐storm sample indicated that an average error of 20–25% is introduced when a single observation is assumed to represent the mean rainout over areas of 10–12 mi2. Correlation analyses indicated that the rainfall at a given point is not strongly related to the radioactive rainout at that point. However, when areal patterns of rainfall and rainout are compared and allowance is made for displacement of high and low centers due to various meteorological influences, a strong association is indicated between the major features of the patterns in most