Some new (2'-5')oligoadenylate trimers, i e . , 22-28, containing the antiviral nucleoside ribavirin ( = 1 -(P-Dribofuranosyl)-1H-l,2,4-triazole-3-carboxamide; 7) and the synthetic cytokine 6-(benzylamino)purine riboside (= N6-benzyladenosine; 1) in different positions of the trimer, have been synthesized by the phosphotriester method. The selectively blocked nucleosides 2-6 and 8-11 and the 2-phosphodiesters 13 and 14, used for the oligonucleotide syntheses, were synthesized from the corresponding unprotected ribonucleosides 1 and 7, and isolated by silica-gel column chromatography. The fully deblocked trimers 22-28 were purified by ion-exchange chromatography on DEAE-ServaceN23-SS. The newly synthesized compounds were characterized by physical means. The ability of synthesized trimers to inhibit HIV-1 replication and to improve RNase L activation were investigated. Some of the synthesized trimers showed also biological inhibition of HIV-1 reverse transcriptase and HIV-1-induced syncytia formation. It was shown that AdoB"-containing trimers inhibited HIV-I-induced syncytia formation > 1500-fold, independently of the position of the AdoB" residue in the olinomer chain.