The present invention is directed to a method for the synthesis of a bi-functional complex comprising a molecule part and an identifier oligonucleotide part identifying the molecule part. A part of the synthesis method according to the present invention is preferably conducted in one or more organic solvents when a nascent bi-functional complex comprising an optionally protected tag or oligonucleotide identifier is linked to a solid support, and another part of the synthesis method is preferably conducted under conditions suitable for enzymatic addition of an oligonucleotide tag to a nascent bi-functional complex in solution.