Use of basin wetlands by breeding populations of 12 species of waterfowl was investigated in 1965 and during 1967-69 throughout the prairie pothole region of North Dakota. Data were obtained primarily by random sampling techniques. Of the total population occupying natural basin wetlands 55 percent occupied seasonal and 36 percent occupied semipermanent wetlands. Seasonal wetlands contained 60 percent of the population of dabbling ducks, while semipermanent wetlands supported 75 percent of the population of diving ducks. On basins with ponded water, highest concentrations of breeding pairs occurred on temporary, seasonal, and semipermanent wetlands; moderate concentrations were recorded on ephemeral, fen, and undifferentiated tillage wetlands, and low concentrations occurred on permanent and alkali wetlands. The proportion of basins that retained ponded water had a direct bearing on the value of each type of wetland to breeding waterfowl. Relative values of the more intermittent types of wetlands are greatly increased during years of ample precipitation.