# Custom sequencing primers on the MiSeq
For reference, see the [MiSeq System Custom Primers Guide](https://support.illumina.com/downloads/miseq-system-custom-primers-guide-15041638.html).
Custom sequencing primer positions:
* Custom Read 1 primer: position 18
* Custom Index Read primer: position 19
* Custom Read 2 primer: position 20
When adding custom primers to the custom primer wells, pipette 600 µl of custom primer at 0.5 µM into the designated well.
**Can only one custom index primer be used?**
* Yes, only index 1 may be custom or standard. Index 2 is primed off the oligo flow cell lawn (see the [Indexed Sequencing Guide](https://support.illumina.com/downloads/indexed-sequencing-overview-15057455.html)).
Alternatively, custom primers can be spiked into the existing Illumina sequencing primers. For further information, search for Knowledge Base article **Spiking custom primers into the Illumina sequencing primers**.
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