Average values of the F1 critical frequency (f0F1) and the height of the F1 ledge (hmF1) for Ibadan (Latitude 7.4 ¿N, Longitude 3.9 ¿E) were used for this study. Well-defined F1 characteristics are observed during winter at low solar activity. International reference ionosphere (IRI) does not predict F1 parameters during this season. Deviation of predicted F1 electron density (N1) by the IRI model from observed values are less than 10% for all seasons of low solar activity, when IRI predicts NF1. Higher percentage deviations are observed during summers of high solar activity. IRI overestimates hmF1. Deviations from experimental values vary from 4 to 35%. ¿ American Geophysical Union 1996