The Klein effect (G. S. Klein, 1964) refers to the finding that high-frequency words produce greater interference in a color-naming task than low-frequency words. The present study used the Klein effect to investigate the relationship between frequency and age of acquisition (AoA) by measuring their influence on color naming. Two experiments showed reliable effects of frequency (though in the opposite direction to that reported by Klein) but no effects of AoA. Experiment 1 produced a dissociation between frequency and AoA when manipulated orthogonally. Experiment 2 produced the same dissociation using different stimuli. In contrast, both variables reliably influenced word naming. These findings are inconsistent with the view that frequency and AoA are 2 aspects of a single underlying mechanism.