The relationship between American College Testing Program (ACT) and California Test of Mental Maturity (CTMM) scores were explored. Four hundred and thirty-four undergraduate subjects of both sexes were selected from a midwestern university. Pearson product moment correlation (r) and Kendall rank correlation coefficient (tau) were used to measure correlations between each standard ACT score and each CTMM score. Factor analyses were performed on several combinations of test scores and subscores. The correlation data suggest that, although the two tests do not approach perfect correlation, they do load significantly on only one factor. Therefore, this study suggests that both the ACT tests and the CTMM are unidimensional scales measuring a common quality which could plausibly be labelled mental ability. (Author/PN)