Analysis of gene expression using real-time reverse transcription polymerase chain reaction (RT-PCR) requires reference genes to normalize expression values between samples. We have developed a novel reference for real-time RT-PCR using an arbitrary primer to amplify a random set of genes. The arbitrary primer amplifies over 30 genes, whose cumulative expression as measured by real-time RT-PCR closely follows that of UBQ 11, an Arabidopsis thaliana gene that is used as a reference on microarrays. The expression of arbitrary genes is also compared with potato (Solanum tuberosum spp. tubersosum) housekeeping genes and was shown to be stable during Phytophthora infestans infection.