Do conceptual categories affect basic visual processing? A conceptual grouping effect for familiar stimuli is reported using a visual search paradigm. Search through conceptually-homogeneous non-targets was faster and more efficient than search through conceptually-heterogeneous non-targets. This effect cannot be attributed to perceptual factors and is not explained by a long-term representational reorganization due to perceptual-learning. Rather, conceptual categories seem to modulate visual representations dynamically, and are sensitive to task-demands. Verbally labeling a visual target further exaggerates the degree to which conceptual categories penetrate visual processing. (Contains 4 figures.)