In order to establish the quantitative parameters indicating serum thyrotropin dynamics after TRH stimulation, we measured the maximum incremants in TSH above the baseline level (max. ⊿TSH), the percentage ratio of the TSH level at 30 min to that at 15 min (R 30/15) and the percentage ratio of the TSH level at 120 min to that at 30 min (R 120/30) in 145 normal children. The geometric means (-2SD and+2SD) of max. ⊿TSH, R 30/15 and R 120/30 were 11.2% (3.9 to 32.5) uU/ml, 101.1% (75.9 to 134.7) and 38.9% (25.8 to 58.5), respectively. The values were compared with those of variables computed from the mathema-
tical model of Okuno et al. (1977), i.e., C=(a/(β-α))•(Q(0)/V)(e(-αt)-e(-βt)＋Coe(-βt)where α=the rate constant for TSH release, β=the rate constant for TSH elimination, and Q(0)/V=the serum TSH releasing value per minute. Highly significant correlations were found between max. ⊿TSH and Q(0)/V (p<0.001), between R 30/15 and α (p<0.001) and between R 120/30 and β (p<0.001). The values of max. ⊿TSH also correlated well with the integrated secretion of TSH (p<0.001). These results suggest that our three parameters are more practical and useful indicators of serum TSH dynamics after TRH stimulation than the cumbersome mathematical model of Okuno et al. (1977), facilitating the detection of mild delayed TSH response.