BDNF and depressive disorder: The results of this study using a highly sensitive BDNF ELISA demonstrate that saliva samples can be used to measure BDNF levels accurately in readily accessible human samples like saliva, thus confirming the very recent results of Ikenouchi et al.12 Correlations can now be readily explored between BDNF levels in human saliva and a range of physiological and pathological conditions of interest, including exercise, ageing, depression and neurodegeneration.