Three tests of intellectual performance capacity referring to factors V, S, and R, according to Thurstone's system of primary mental abilities were administered to a total number of 34 subjects. Immediately after finishing an individual item, subjects were asked to estimate the perceived difficulty of that item. The ratings were to be given on a symmetrical scale with 9 categories with verbal expression labels. A high correlation between the rank order of items according to estimated difficulty and the real item sequence was obtained in all three tests used. A linear relationship was found between estimated difficulty and standard scores corresponding to solution frequencies. A close correspondence was noticed between the widths and the levels of the ranges of the estimates on the one hand and the corresponding widths and levels of the standard score ranges on the other hand. Subjects who could solve an item correctly tended to estimate the difficulty of that item as lower than subjects who could not. (Author)