1. Plasma catecholamine (CA) levels were examined in rats exposed to SART (specific alternation of rhythm in temperature) stress, a repeated cold stress. Effects of neurotropin, a sedative analgesic, and alprazolam, an anxiolytic, on the changes in plasma and brain CA levels were then studied. 2. SART stress induced remarkable increases in plasma levels of noradrenaline (NA) and dopamine (DA). The plasma adrenaline (Adr) level also increased significantly, but the extent was smaller than that of NA or DA. 3. Repeated treatments with neurotropin reduced the stress-induced increases in plasma and brain NA and DA levels significantly and dose-dependently. 4. Repeated treatments with alprazolam markedly reduced all increases in plasma and brain CA levels. 5. The above findings suggest that SART-stressed animals are in an increasing state of sympathetic neuronal activity and in a slightly increasing state of adrenal function. Neurotropin is also suggested to have modulating effects on autonomic imbalance in both catecholaminergic and cholinergic nerves.