# Are custom primers loaded as a pool or individually on the iSeq 100?

For the iSeq 100, custom primers are loaded individually for each read. For more information, see the [iSeq 100 Sequencing System Guide](https://support.illumina.com/downloads/iseq-100-system-guide.html), and search Knowledge Base article **Spiking custom primers into the Illumina sequencing primers**.

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