Amino acids have received increased attention with regard to their thermoregulatory effects and possible role as neurotransmitters within the thermoregulatory system. The purpose of the present work was to evaluate in conscious rabbits the changes in cerebrospinal fluid (CSF) concentration of taurine, GABA, aspartate, and glutamate during exposure to high ambient temperature (50 min, 40°C) to investigate their involvement in heat stress (HS). CSF and plasma osmolality and CSF concentrations of some cations and proteins were also determined. HS animals underwent transient hyperthermia and thereafter fully recovered. This was accompanied by a significant rise in CSF and plasma osmolality, CSF protein, calcium, taurine, and GABA. Artificial CSF osmolality measurements after addition of CaCl₂ or taurine demonstrated that the increased CSF osmolality after HS is accounted for, only in part, by the increased concentrations of either calcium and taurine. It is suggested that, during HS, taurine and GABA are released in the extracellular space of brain tissues in higher amounts, possibly to counteract the resulting hyperthermia.