In Drosophila, as in mammalian cells, the Raf serine/threonine kinase appears to act as a common transducer of signals from several different receptor tyrosine kinases. We describe a new role for Raf in Drosophila development, showing that Raf acts in the somatic follicle cells to specify the dorsoventral polarity of the egg. Targeted expression of activated Raf (Rafgof) within follicle cells is sufficient to dorsalize both the eggshell and the embryo, whereas reduced Raf activity ventralizes the eggshell. We show that Raf functions downstream of the EGF receptor to instruct the dorsal follicle cell fate. In this assay, human and Drosophila Rafgof are functionally similar, in that either can induce ventral follicle cells to assume a dorsal fate.