Biographies of great achievers, in science as well as other disciplines, suggest that those of genius caliber possess, in addition to their intellectual gift or gifts, an extraordinary abundance of mental energy. They can focus their attention on some task for long periods without tiring or becoming distracted from the problem at hand. It is plausible to suppose that intellectual achievement is a function of the product, rather than the sum, of mental talent and mental energy. It is therefore surprising that no standardized measure or method of assessing mental energy has been developed. One obvious approach would employ a variety of self-report items similar to those suggested. Perhaps other methods of assessing mental energy are feasible and might usefully augment current methods of predicting academic and occupational success.