The visual search time for the presence of both of two physical stimuli was measured under two conditions: (1) conceptual identity-the targets being upper and lower case forms of the same letter (C.1); and (2) upper and lower case forms of different letters (D). It was hypothesized that C.1 would facilitate the simultaneous analysis of the features of two letters in a visual display. Each subject searched for the two classes of stimuli on alternate days. Responses in the C.1 condition were found to be significantly faster than in the D condition. RT was shorter for an affirmative than for a negative response, but there was no interaction between conditions and affirmative or negative responses. The results are considered in relation to the concept of categorizing.