Quantificational determiners in Japanese can be marked with genitive case. Current analyses (for example by Watanabe, Natural Language and Linguistic Theory, to appear) treat the genetive case marker in these cases as semantically vacuous, but we show that it has semantic effects. We propose a new analysis as reverse partitives. Following Jackendoff (MIT-Press, 1977), we assume that partitives always contain two NPs one of which is phonologically deleted. We claim that, while in normal partitives the higher noun is deleted, in reverse partitives the lower noun is deleted.