Experimental values of the critical frequencies of the ionosphere (f0E, f0F1, and f0F2) obtained at South American stations for different solar conditions and seasons are used to check the validity of the international reference ionosphere model to predict these ionospheric variables in this region. The results obtained show that, in general, for f0E and f0F1 there is good agreement between the predicted and experimental values when compared. The model predicts f0F1 for periods when F1 was not present. The degree of accuracy among experimental and predicted f0F2 values is lower than those observed for the other characteristics, and cases with strong disagreement are observed. It is shown that in some cases a large error would be produced if the predicted f0F2 is used as an input to a total electron content model. ¿ American Geophysical Union 1998