Abstract Negative concord (NC) is used in many English varieties but usually considered ungrammatical in ‘standard’ contemporary English, where negative polarity items (NPIs) are used. In this paper, we take a novel experimental approach to the use of NC versus NPI constructions, in relation to register, sets of speech repertoires linked to specific situational and functional parameters. We report on two rating experiments with American and British English participants using interlocutor relations as a formality manipulation. Results show that (i) across both samples, NC constructions were rated as less appropriate than NPI associates, and (ii) there was a register effect in the American English data in that NC was rated less appropriate in formal than informal contexts. Our study is the first to provide experimental evidence for the register-sensitivity of NC constructions in American English.