There has been an unprecedented interest in the modulatory effects of intranasal oxytocin on human social cognition and behaviour, however as yet no study has actually demonstrated that this modality of administration increases concentrations of the peptide in the brain as well as blood in humans. Here using combined blood and cerebrospinal fluid (CSF) sampling in subjects receiving either 24 IU of oxytocin (n = 11) or placebo (n = 4) we have shown that oxytocin levels significantly increased in both plasma and CSF. However, whereas oxytocin plasma concentrations peaked at 15 min after intranasal administration and decreased after 75 min, CSF concentrations took up to 75 min to reach a significant level. Moreover, there was no correlation (r = <0.10) between oxytocin plasma and CSF concentrations. Together, these data provide crucial insights into the plasma and CSF kinetics of intranasally administered oxytocin.