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Description: To test the limits of parallel processing in vision, we investigated whether observers can recognize two words at once. Observers viewed brief, masked pairs of words and were instructed in advance to judge both of the words (dual-task condition), or just one of the words (single-task condition). For judgments of semantic category, the dual-task deficit was so large that it supported serial processing: observers could only recognize one word and had to guess about the other. Moreover, observers were more likely to be correct about one word if they were incorrect than correct about the other, which supports a serial switching model. In contrast, judgments of text color with identical stimuli were consistent with unlimited-capacity parallel processing. Thus, under these conditions, serial processing is necessary to judge the meaning of words but not their physical features. Further investigation must address the implications of this result for natural reading.