Involvement of the biogenic amines—acetylcholine, epinephrine, norepinephrine, dopamine, serotonin, and γ-aminobutyric acid—in behavioral states through neurotransmission is appraised. An accessory role is favored for acetylcholine because its distribution and function in the brain are less specific than those of norepinephrine or serotonin, which are concerned with REM and deep sleep, while epinephrine is concerned with brain stem activity in wakeful and (or) aggressive arousal. Decreased brain metabolism of norepinephrine and serotonin has been correlated with conditions favoring aggression. Norepinephrine and acetylcholine are implicated in neurochemical coding which regulates food and water intake. γ-Aminobutyric acid and other amino acids can facilitate or inhibit neural transactions. The precursor to dopamine alleviates Parkinsonian tremor. Aberrant catecholamine metabolism and structural differences in related psychotomimetic substances are considered in the etiology of schizophrenia, depression, and similar affective disorders. Other states of impaired behavior are also linked with altered biogenic amine chemistry.