Yolk proteins are transported from the hemolymph into the oocytes of insects during vitellogenesis by receptor-mediated endocytosis. Since other hemolymph proteins, both native and foreign, are not accumulated in the oocyte, the process of uptake is selective for yolk proteins. Peptide domains within the yolk proteins must therefore be involved in receptor recognition. With the long-term aim of identifying these domains and to open the possibility of understanding the molecular basis of receptor-mediated endocytosis of yolk proteins, we began investigating how well this mechanism has been conserved in evolution. We studied the uptake of yolk proteins from 13 different Drosophila species and five other dipteran species, namely, Calliphora erythrocephala, Sarcophaga argyrostoma, Musca domestica, Lucilia servicata, and Protophormia terrae-novae, into the ovaries of Drosophila melanogaster and Drosophila funebris. The results from these experiments showed that in all cases the foreign yolk proteins were taken up by the host ovaries, indicating that the mechanism and peptide domains of the yolk proteins involved in recognition of the receptor have been well conserved in dipteran evolution.