Multiple regression equations predicting first semester grade point average (GPA) from high school percentile rank (HSPR) and Composite score on the American College Test (ACT:C) were examined for five successive fall freshman classes (1965-1969) at the University of Illinois. Slopes were significantly different among the five equations. Further analysis indicated a systematic decline in the ACT:C regression coefficients over time while the HSPR coefficients remained approximately constant. Possible explanations advanced for these findings were unequal test score intervals, a low GPA ceiling, and changes in the GPA criterion. (Author)