Three experiments investigated performance for words which differ from another word only by the transposition of two letters (e.g.,salt, slat). In Experiment 1, high frequency words from transposed-letter (TL) confusable pairs were responded to more slowly than carefully matched control words in both the lexical decision and word naming task. Low frequency TL words were responded to less accurately than control words in the naming but not the lexical decision task. Experiment 2 replicated the naming data of Experiment 1 and also revealed that naming accuracy for TL word targets was reduced when they were preceded by a brief masked presentation of their confusable mate. Experiment 3 provided a third replication of the impaired naming performance for TL target words and demonstrated that the effect was insensitive to concurrent dual task demands. These TL confusability effects provide strong constraints that can contribute to evaluation and specification of current models of visual word recognition.