This study investigates how newly learned words are integrated into the first-language lexicon using masked priming. Two lexical decision experiments are reported, with the aim of establishing whether newly learned words behave like real words in a masked form priming experiment. If they do, they should show a prime lexicality effect (PLE), in which less priming is obtained due to form similarity when the prime is a word. In the first experiment, subjects were taught the meanings of novel words that were neighbors of real words, but no PLE was observed; that is, equally strong form priming was obtained for both trained and untrained novel primes. In the second experiment, 4 training sessions were spread over 4 weeks, and under these conditions, a clear PLE was obtained in the final session. It is concluded that lexicalization requires multiple training sessions. Possible explanations of the PLE are discussed.