Using 2',3'-O-[4-N-(2-chloroethyl)-N-methylamino]benzylydene derivatives of AUGUn [32P]pC and 4-[N-(2-chloroethyl)-N-methylamino]benzylmethylphosphoamide derivatives of [32P]pAUGUn, the affinity labelling of human placental 40S ribosomal subunits was studied within 40S initiation complexes obtained in the presence of a ternary complex eIF-2.GTP.Met-tRNA(fMet). Analysis of the ribosomal proteins labelled by these mRNA analogues revealed that proteins S3/S3a, S6, S7, and S14/S15 play a key role in the interaction of the template with the 40S subunit in the presence of the ternary complex eIF-2.GTP.Met-tRNA(fMet). Proteins S2, S4, S5, S8, S9, and S17 are also involved in this interaction.