Which NP does all associate with in “The pandas, the children have all seen”, the pandas or the children, or both? The intuition of adult Mandarin native speakers regarding the interpretation of the adverbial quantifier dou ‘all’ remains unclear and controversial, and based on these unclarities, various incommensurate theories of domain selection have been proposed. This paper points out that previous studies were confused by dou-domain selection because they used non-optimal testing materials. We present experiments on adults’ interpretation of dou, designed to avoid these pitfalls to test predictions of several influential theories. Despite extensive theoretical proposals in the literature, this is the first experimental study of adult knowledge and use of syntactic constraints on the quantifier domain of dou. We advance the hypothesis that the quantifier dou can take one and only one c-commanding NP as its domain, and an analysis based on a locality restriction are not operative in the domain we explore.