This study investigated gene expression changes in whole blood samples obtained from donors diagnosed with major depressive disorder (MDD) compared to healthy controls. Micro-array data were available from whole blood on patients with MDD (N=128, 64 with generalised anxiety disorder, diagnosed by the MINI questionnaire, and 64 without anxiety disorder) and healthy controls (N=64). RNA was isolated from all samples using the standard PAXgene protocol on the Qiagen Biorobot 8000. All samples gave good quality RNA, as assessed by Agilent Bioanalyser. The yield range was 0.86-15.05ug with an average of 6.25ug. Samples were then randomised into batches, with each batch containing a representative number of controls, depression with anxiety and depression without anxiety, and the same ratio of females to males (3:1). 50ng of RNA from each sample was converted to a biotin labeled cDNA probe using NuGEN SPIA amplification. The probes were then hybridized to Affymetrix U133_Plus2.0 Genechips.