Variations in morning plasma cortisol are associated with quantitative traits including blood pressure and glucose, serum lipid profile, mood and memory. Morning plasma cortisol is a heritable trait but little is known of the genes that contribute. To identify such genes we have undertaken cortisol measurements and genome wide association studies (GWAS) in ~3000 participants from 3 cohorts. Initial results are promising, identifying two loci in which the top hit SNPs are associated with cortisol to pless than 10-8. We have therefore established the CORtisol NETwork (CORNET) in order to: (i) extend GWAS with morning cortisol to n=10,000; (ii) genotype top hit SNPs in at least two replication cohorts, in which additional measurements of dynamic control of cortisol are available; and (iii) resequence loci around top hits to identify rarer variants contributing to cortisol variation. The results will provide novel insights into pathways leading to cardiometabolic and neuropsychiatric disease.