The assumptions of the classical test-theory model are used to develop a theory of reliability for criterion-referenced measures which parallels that for norm-referenced measures. It is shown that the Spearman-Brown formula holds for criterion-referenced measures and that the criterion-referenced reliability coefficient can be used to correct criterion-referenced correlations for attenuation. A formula is developed which expresses the criterion-referenced reliability coefficient in terms of the mean, variance, and norm-referenced reliability coefficient. The implications of the resulting formula are discussed. (Author/DG)