In pursuing the mapping between syntax and phonology/prosody, little attention has been paid to the kinds of syntactic information that can affect prosody. In this paper, we explore Japanese downstep, a process in phrasal phonology. What syntactic information affects downstep and what does not? Specifically, do lexical categories affect downstep? We investigate the effects of nouns, adjectives, and verbs in different syntactic settings (e.g., [X1 [X2 N]], [[X1 X2] N], predicative X) through production experiments. We found that adjectives in [X1 [X2 N]] may block downstep, whereas adjectives in other structures as well as nouns and verbs generally do not block it. We analyze this phonological patterning as being derivative of an interaction between syntactic structures and lexical categories.