This paper uses experimental methodology to examine NPs in generic environments in English and Brazilian Portuguese. According to the semantic literature, NPs obtain generic readings from two sources: generic sentences ('Lions are dangerous') and kind-reference ('Dodo birds are extinct'). English and Brazilian Portuguese are known to differ in the types of NPs that are allowed in the two types of environments, but there is disagremeent in the literature concerning (1) the status of bare (article-less) NPs in generic environments in Brazilian Portuguese; and (2) whether singular and/or plural generics are restricted to well-defined kinds cross-linguistically. The broader goal of this paper is to use experimental methodology to resolve these disagreements; the more specific goal is to test the theoretical proposal of Dayal (2004), which makes testable predictions for the distribution of generic NPs cross-linguistically. The results of Acceptability Judgment Tasks with native speakers of English and Brazilian Portuguese provide support for Dayal's proposal that plural generics cross-linguistically denote kinds, while definite singular generics denote taxonomic entities. These findings highlight the value of experimentally testing the predictions of semantic theories.