Age differences in intellect as reflected by performance on the Wechsler Adult Intelligence Scale (Revised) (WAIS-R) were evaluated for persons aged 20 to 74 years. Educational attainment levels were held constant. The WAIS-R sample included 1,480 men and women in the following seven age groups--20-24 years (n=250), 25-34 years (n=250), 35-44 years (n=250), 45-54 years (n=250), 55-64 years (n=160), 65-69 years (n=160), and 70-74 years (n=160). The 25-34 year age group served as the target sample for this study; the mean scores for adults in each educational category, within each age group, were weighted to match the educational distribution of ages 25-34 years. After weighting for education, the decline in verbal intelligence quotient (IQ) from age to age disappeared. However, declines across the 20-74 year range remained for performance IQ and full scale IQ, even after controlling for education. These results were also obtained using multiple regression techniques. The impact of education on each of the 11 subtests was also evaluated; the results were interpreted as supportive of J. L. Horn's fluid-crystallized explanation of changes in intelligence with advancing age. Seven data tables and 14 graphs are included. (TJH)