The changes occurring on the J. T. Curtis Prairie, an artificial prairie in the University of Wisconsin Arboretum, were studied by means of four surveys spaced at 5—year intervals. Frequency data from more than 650 meter—square quadrats with known locations were obtained at each survey. Five stands, delimited on the basis of their compositional index (CI) as determined by indicator species, were compared with native prairies having similar CI values by means of species lists and sum frequency of the species. When prairie species only are considered, some artificially established stands are as similar to native stands as native stands is the presence of large numbers of non—prairie species. The artificial stands have much larger species lists and higher sum frequencies than native prairies. The results indicate that the Curtis Prairie is becoming very similar to native prairies in numbers and species of prairie plants, and that the non—prairie species are materially reduced in importance.