Staining hundreds to thousands of RNA species each of which requires tens of unique encoding probes requires a very large number of unique oligonucleotide sequences. The sheer number of unique sequences makes traditional solid phase oligonucleotide synthesis prohibitively expensive in most cases. For example, assuming a modest cost of $0.10\/base, an encoding probe length of ~100 nt, and the need for ~50,000 unique oligos for a single MERFISH measurement, the cost of the needed oligos would be $500,000! To circumvent this astronomical cost, we have developed a high-throughput approach to generating these probes which utilizes array-derived synthesis of complex oligonucleotide pools. These arrayderived complex oligonucleotide pools that contain ~100,000 custom designed sequences can be purchased for only a few thousand dollars. The challenge to using these pools is that each individual sequence is provided in quantities far too small to be used directly for labeling. Thus, we developed an enzymatic amplification protocol to generate the encoding probes in high quantity sufficient for RNA FISH experiments using the array-derived complex oligonucleotide pools as templates.