Abstract: Substituted propargylethoxyamido nucleosides are disclosed having the structure ##STR1## wherein X is selected from the group consisting of amino alkanoic acid, alkylamino benzoic acid, .alpha.-amino acid, and 4-amino-2-butynoic acid. R.sub.1 and R.sub.2 taken separately are selected from the group consisting of --H, lower alkyl, protecting group, and label; R.sub.3 is selected from the group consisting of --H and lower alkyl. B is a 7-deazapurine, purine, or pyrimidine nucleoside base. When B is purine or 7-deazapurine, the sugar moiety is attached at the N.sup.9 -position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N.sup.1 -position of the pyrimidine.