In two experiments, subjects searching for the letter t in passages that contained some misspellings made many more errors on the word the than on other correctly spelled words. Accuracy increased dramatically when the word the and the other words containing t were misspelled, even when the misspelled word was the same shape as the original. These findings define a word-inferiority effect, which stands in contrast to the superior perception of letters in words over nonwords commonly found in tachistoscopic studies. In a third experiment, subjects searched for the letter n in passages typed normally or typed with all interword spaces replaced by the symbol +. Detection errors on the word and were greatly reduced when the interword spaces were replaced by +s, but errors on other words, including those ending in the suffix morpheme -ing, were not affected by this manipulation. These results suggest that frequent function words are processed in terms of reading units that are larger than the letter and include the interword spaces.