Triiodothyronine (T3) receptor kinetics were determined in liver nuclei isolated from fasting and fed rats. The results indicate that although affinity equilibrium constants (Ka) did not differ in the two groups, mean (+/- SE) maximal binding capacity (MBC) was reduced significantly to .30 +/- .05 nM/mg DNA in fasting compared to .46 +/- .07 nM/mg DNA (p less than .01) in the fed state. This observed decrease in MBC during fasting apparently could not be accounted for by a differential rates of loss of either DNA or of the receptor during the period of incubation.