Thyronamines (TAMs) are a newly identified class of endogenous signaling 
compounds. Their structure is identical to that of thyroid hormone and 
deiodinated thyroid hormone derivatives, except that TAMs do not possess a 
carboxylate group. Despite some initial publications dating back to the 1950s, 
TAMs did not develop into an independent area of research until 2004, when they 
were rediscovered as potential ligands to a class of G protein-coupled receptors 
called trace-amine associated receptors. Since this discovery, two 
representatives of TAMs, namely 3-iodothyronamine (3-T(1)AM) and thyronamine 
(T(0)AM), have been detected in vivo. Intraperitoneal or central injection of 
3-T(1)AM or T(0)AM into mice, rats, or Djungarian hamsters caused various prompt 
effects, such as metabolic depression, hypothermia, negative chronotropy, 
negative inotropy, hyperglycemia, reduction of the respiratory quotient, 
ketonuria, and reduction of fat mass. Although their physiological function 
remains elusive, 3-T(1)AM and T(0)AM have already revealed promising therapeutic 
potential because they represent the only endogenous compounds inducing 
hypothermia as a prophylactic or acute treatment of stroke and might thus be 
expected to cause fewer side effects than synthetic compounds. This review 
article summarizes the still somewhat scattered data on TAMs obtained both 
recently and more than 20 yr ago to yield a complete and updated picture of the 
current state of TAM research.