This paper examines a type of dou quantification found in wh-questions such as ta dou mai le shenme? ‘What are all the things that he bought?’ This type is different from the well-known dou quantification in that the leftness condition cannot be applied to the former. I propose that the former type of quantification is subject to the topic-focus structure rather than to the syntactic structure, which means that the domain of the quantification is determined in relation to 'old' and 'new' information of a sentence. Sentences including dou can be divided into topic and focus, and each part is mapped onto the restrictor and the nuclear scope in a tripartite structure of dou quantification. This analysis accounts for the reason why a list answer is appropriate to questions with dou, why wh-words in the questions cannot be quantity expressions, and why wh-words should either have a plural interpretation or take the plural form. This analysis also explains the distribution of dou, i.e., dou should c-command a focused phrase. Finally, I point out that the analysis can extend to declaratives which are rare but still observable, and that the two types of dou quantification can arise simultaneously