The concentration of plasma and intracerebral cortisol in pigs challenged with 0.5 IU adrenocorticotrophic hormone/kg body weight was simultaneously measured at a 30 min rate. The pigs (n=5) were provided with indwelling jugular vein catheters and guide canullas for insertion of a hippocampal microdialysis probe. Every five blood samples taken at 6 min intervals were pooled to simulate the 30 min collection time of the microdialysis. Stimulation resulted in an increment of cortisol of roughly 200% in plasma and 190% in the dialysate compared to basal value. The average time lag of hippocampal to plasma peak was 48.75 min. Considering the temporal resolution of the protocol it is inferred that delays of at least 30 min occur between variations of peripheral and central nervous cortisol.