This study attempts to specify the contribution of two subregions of Broca's area during syntactic and semantic processing of sentences by examining brain activation in a grammaticality judgment task. The processing of two types of ungrammatical sentences was examined. One type leaves the thematic interpretation generally unaffected, by violating the noun-verb agreement in number, while the other type introduces an extraneous verb, which cannot be incorporated into the developing thematic structure. Pars triangularis was more sensitive to the extra verb violation, whereas pars opercularis was more sensitive to the noun-verb agreement violation. The current study adds to the growing literature that suggests there are separable functional subregions of Broca's area, with pars triangularis more involved in thematic processing and pars opercularis more involved in syntactic processing. The posterior left temporal area was also involved in both types of processing.