A method of forming a conjugate between an antibody peptide and a modifying group, wherein said modifying group is covalently attached to said antibody peptide through an intact glycosyl linking group, said antibody peptide comprising a glycosyl residue having the formula: wherein a, b, c, d, i, j, k, l, q, r, s, t, u, and z are members independently selected from 0 and 1; m is independently selected from 0 and 1, or m is independently selected from 0 - 20, when said antibody peptide is anti HER2 antibody peptide; e, f, g, and h are members independently selected from the integers from 0 to 4; n, v, w, x, and y are 0; R is a modifying group, a mannose or an oligomannose; and R' is a member selected from hydrogen and a glycosyl residue, a glycoconjugate, and a modifying group, and wherein, when said antibody peptide comprising a glycosyl residue is an anti-RSV F peptide, it has the formula: wherein a - z, R and R' are as defined above, and p is independently selected from 0 and 1; said method comprising: (a) contacting said antibody peptide with a glycosyltransferase and a modified glycosyl donor, comprising a glycosyl moiety which is a substrate for said glycosyltransferase covalently bound to said modifying group, under conditions appropriate for the formation of said intact glycosyl linking group, wherein said modifying group is poly(ethylene glycol), preferably linear or branched poly(ethylene glycol), preferably a poly(ethylene glycol) having a homo-disperse molecular weight distribution. a, b, c, d, i, j, k, l, q, r, s, t, u, and z are members independently selected from 0 and 1; m is independently selected from 0 and 1, or m is independently selected from 0 - 20, when said antibody peptide is anti HER2 antibody peptide; e, f, g, and h are members independently selected from the integers from 0 to 4; n, v, w, x, and y are 0; R is a modifying group, a mannose or an oligomannose; and R' is a member selected from hydrogen and a glycosyl residue, a glycoconjugate, and a modifying group, and wherein, when said antibody peptide comprising a glycosyl residue is an anti-RSV F peptide, it has the formula: a - z, R and R' are as defined above, and p is independently selected from 0 and 1; said method comprising: (a) contacting said antibody peptide with a glycosyltransferase and a modified glycosyl donor, comprising a glycosyl moiety which is a substrate for said glycosyltransferase covalently bound to said modifying group, under conditions appropriate for the formation of said intact glycosyl linking group, wherein said modifying group is poly(ethylene glycol), preferably linear or branched poly(ethylene glycol), preferably a poly(ethylene glycol) having a homo-disperse molecular weight distribution. (a) contacting said antibody peptide with a glycosyltransferase and a modified glycosyl donor, comprising a glycosyl moiety which is a substrate for said glycosyltransferase covalently bound to said modifying group, under conditions appropriate for the formation of said intact glycosyl linking group, wherein said modifying group is poly(ethylene glycol), preferably linear or branched poly(ethylene glycol), preferably a poly(ethylene glycol) having a homo-disperse molecular weight distribution.