Travelling to Berlin, he denounced the Haggadah as containing blasphemies against Christianity, causing Frederick I of Prussia temporarily to suspend sales of a recently published edition of the Midrash Rabbah, until a theological investigation had officially pronounced it harmless.
The De Rossi Manuscript No. 541, at Parma, was discovered by S. Buber to contain, among other things, midrashim on four of the five "megillot": Canticles, Book of Ruth, Lamentations, and Ecclesiastes; these he published (Berlin, 1894) under the title of "Midrash Zuṭa," to distinguish them from the "Midrash Rabbah."