A polyacrylamide support as defined in claim 12, wherein the polyacrylamide support with attached oligonucleotides has the formula ##STR57## wherein M is --NH-- or oxygen;a is 0 or 2 to 6; b is 0 or 2 to 6 when M is --NH-- or b is 0 to 6 when M is --O--; c is 1; A is a linking group selected from the group consisting of --(CHR)m --, --C6 H4 --, --C6 H10 --, --(CHR)m C6 H10 --, and --C6 H10 (CHR)m