Coupling efficiencies for the covalent attachment of oligonucleotides (17–29 bases in length) to solid supports derivatized with alkyl-amino and -carboxylic functionalities have been determined. Attachment efficiencies of 60–80% were obtained for coated long-chain alkylamino controlled pore glass (CPG) supports. Similar efficiencies of immobilization were observed for carbox-yl-bearing supports, which additionally exhibited lower levels of non-covalent binding. The extent of terminally linked oligonu-cleotide was determined to be 50–55% of the overall attachment in the carbodiimide-mediated coupling reaction of a 5′-aminohexyl phosphoramidate derivative of a 29-mer to Sephacryl carboxyl support. While lower overall efficiencies of attachment were obtained in the reaction with Sephacryl N-hydroxysuccinimide-activated carboxyl support, greater than 80% of this coupling results in end-attached oligonucleotides.