This paper explores the lengthening of monomoraic nouns in Japanese. An experiment has revealed that monomoraic nouns are lengthened by about 40L50% and/or followed by pauses when not suffixed with monomoraic case markers. The phenomenon is specific to one-mora nouns since bimoraic nouns do not undergo a similar amount of lengthening even without particles. Moreover, monomoraic nouns preceded by adjective phrases of up to three moras show neither lengthening nor pause insertion equivalent to that of sentence-initial monomoraic nouns. This suggests that an adjective phrase plus a monomoraic noun forms a single phonological word of three or four moras. The results suggest that in Japanese one or more lexical words can form an independent phonological word composed of two to four moras. (C) 2002 Elsevier Science Ltd. All rights reserved.