More than ten different protein factors are involved in initiation of protein synthesis in eukaryotes. For binding of initiator tRNA and mRNA to the 40S ribosomal subunit, the initiation factors eIF-2 and eIF-3 are particularly important. They consist of several different subunits and form stable complexes with the 40S ribosomal subunit. The location of eIF-2 and eIF-3 in these complexes as well as the interactions of the individual components have been analyzed by biochemical methods and electron microscopy. The results obtained are summarized in this article, and a model is derived describing the spatial arrangement of eIF-2 and eIF-3 together with initiator tRNA and mRNA on the 40S subunit. Conclusions on the location of functionally important sites of eukaryotic small ribosomal subunits are discussed with regard to the respective location of these sites in the prokaryotic counterpart. © 1991.