The reading level of representative samples of patient education materials obtained from public foundations, pharmaceutical manufacturers, hospitals, and commercial sources was determined according to three readability tests: Fry Readability Graph, Gunning Fog Index, and McLaughlin SMOG Grading Formula. The average reading levels ranged from grade 8.0 for foundation-sponsored materials to grade 9.9 for materials developed by pharmaceutical manufacturers. These levels are higher than the estimated average reading level of the American public. The calculation of correlation coefficients between each of the three methods, using a linear regression equation, indicates that the readability formulas do not correlate well with one another. Although these formulas may provide a convenient method to estimate the reading level, any one formula may not be appropriate for the evaluation of all health-related materials. Educational materials should be tested for readability and comprehension in sample populations before being accepted for general use.