... , less than 0.0004, and 0.22%, respectively. 3'-Monoiodothyronine cross-reacted 1.7%. Serum 3',5'-T2 concentrations were (mean +/- SD) 6.4 ... 45% at 1 h. Total fasting in 3 obese subjects was associated with a significant increase in serum 3',5'-T2 from 8.6 to ... in serum of normal man. The various data suggest that: 1) 3',5'-T2 is a normal component of human serum; 2) almost ...