Cortisol is one of the primary mediators of the stress response, in the main having immunosuppressive effects. An important component of the host response in periodontal inflammation is gingival crevicular fluid (GCF), with constituents mainly derived from serum. Cortisol, like many other steroids, is present in saliva but its occurrence in GCF does not seem to be documented. Unstimulated whole saliva was collected and GCF was sampled on filter disks. The samples were analysed by a modified RIA method for serum in such a way that small volumes and low concentrations could be measured. Our findings suggest that the total concentration of cortisol in GCF might be estimated to levels below 1/10 of that in serum. However, what appears as a distinctive feature is the considerable variation of the cortisol concentrations for individual teeth. To our knowledge, this is the first time cortisol has been measured in gingival crevicular fluid, and this opens the prospects for further in vivo research.