We conducted a study on variation in the human peripheral blood transcriptome using the PAXgeneTM Blood RNA System (PreAnalytix) and GeneChip Human Genome U133 plus 2.0 Array (Affymetrix). Data regarding the RNA integrity number (RIN) and complete blood count (CBC) for each healthy individual were collected and combined with gene expression profiles to characterize both biological and technological variation. The effect of RNA sample degradation on microarray performance in peripheral blood transcriptome analysis was also investigated.