An oligomer comprising a sequence of morpholino subunits, each supporting a base-pairing moiety, such that said oligomer can bind in a sequence-specific manner to a target nucleic acid, wherein said subunits are joined by phosphorus-containing intersubunit linkages having the structure: where W is S or O, X = NR 1 R 2 or OR 6, Y = O or NR 7, and each said linkage is selected from: (a) uncharged linkage (a), where each of R 1, R 2, R 6 and R 7 is independently selected from hydrogen and an alkyl radical of one to six carbon atoms; cationic linkage, where X = NR 1 R 2 and Y = O, and NR 1 R 2 represents an optionally substituted piperazino group, such that R 1 R 2 = -CHRCHRN(R 3)(R 4)CHRCHR-, where each R is independently H or CH 3, R 4 is H, CH 3 or an electron pair, and R 3 is selected from H, an alkyl radical of one to six carbon atoms, C(=NH)NH 2, Z-L-NHC(=NH)NH 2, and {C CHR'NH} m H, where Z is carbonyl (C) or a direct bond, L is an optional linker up to 18 atoms in length having bonds selected from alkyl, alkoxy, and alkylamino, R' is a side chain of a naturally occurring amino acid or a one- or two-carbon homolog thereof, and m is 1 to 6; cationic linkage, where X = NR 1 R 2 and Y = O, R 1 = H or CH 3, and R 2 = LNR 3 R 4 R 5, where L, R 3, and R 4 are as defined above, and R 5 is H, an alkyl radical of one to six carbon atoms, or lower (alkoxy)alkyl; and cationic linkage, where Y = NR 7 and X = OR 6, and R 7 = LNR 3 R 4 R 5, where L, R 3, R 4 and R 5 are as defined above, and R 6 is H or an alkyl radical of one to six carbon atoms; and 20% to 50% of said linkages of the oligomer are selected from cationic linkages,, and. W is S or O, X = NR 1 R 2 or OR 6, Y = O or NR 7, (a) uncharged linkage (a), where each of R 1, R 2, R 6 and R 7 is independently selected from hydrogen and an alkyl radical of one to six carbon atoms; cationic linkage, where X = NR 1 R 2 and Y = O, and NR 1 R 2 represents an optionally substituted piperazino group, such that R 1 R 2 = -CHRCHRN(R 3)(R 4)CHRCHR-, where each R is independently H or CH 3, R 4 is H, CH 3 or an electron pair, and R 3 is selected from H, an alkyl radical of one to six carbon atoms, C(=NH)NH 2, Z-L-NHC(=NH)NH 2, and {C CHR'NH} m H, where Z is carbonyl (C) or a direct bond, L is an optional linker up to 18 atoms in length having bonds selected from alkyl, alkoxy, and alkylamino, R' is a side chain of a naturally occurring amino acid or a one- or two-carbon homolog thereof, and m is 1 to 6; each R is independently H or CH 3, R 4 is H, CH 3 or an electron pair, and R 3 is selected from H, an alkyl radical of one to six carbon atoms, C(=NH)NH 2, Z-L-NHC(=NH)NH 2, and {C CHR'NH} m H, where Z is carbonyl (C) or a direct bond, L is an optional linker up to 18 atoms in length having bonds selected from alkyl, alkoxy, and alkylamino, R' is a side chain of a naturally occurring amino acid or a one- or two-carbon homolog thereof, and m is 1 to 6; cationic linkage, where X = NR 1 R 2 and Y = O, R 1 = H or CH 3, and R 2 = LNR 3 R 4 R 5, where L, R 3, and R 4 are as defined above, and R 5 is H, an alkyl radical of one to six carbon atoms, or lower (alkoxy)alkyl; and cationic linkage, where Y = NR 7 and X = OR 6, and R 7 = LNR 3 R 4 R 5, where L, R 3, R 4 and R 5 are as defined above, and R 6 is H or an alkyl radical of one to six carbon atoms; and 20% to 50% of said linkages of the oligomer are selected from cationic linkages,, and.