A series of the novel pyrimidine (3–6) and purine (12–15, 18–21) acyclic nucleoside analogues in which the sugar moiety was replaced by a sterically con-strained Z-4-amino-, 4-aminohydrochloride-2-butenyl, or aliphatic 4-aminohydrochloride-2-butyl moiety were syn-thesized and evaluated for their anti-viral and cytostatic activity potency. Cytostatic evaluation of the novel com-pounds on selected panel of human tumour-cell lines showed that the majority of compounds exerted a non-specific anti-proliferative effect at the highest tested con-centration (i.e. 1 9 10 -4 M) against all cell lines. Never-theless, a rather moderate but selective anti-proliferative effects on HeLa cell cultures in comparison to normal fibroblasts WI 38, were observed for compounds 15 and 21. No anti-viral activity was observed, except for compounds 3, 4, 5 and 19 that showed anti-HIV activity at 50% effective concentration ranging between 10 and 96 lM.