Uptake of radiodine by thyroid glan within 90 min after I.v injection with Na 131 I was studied in male rats which had been i.p injected with either PGB1, PGF1α or PGF2α. The mathematical analysis of radioiodide plasma disappearance curves showed that the rioiodide was kinetically exchanged within a two compartmental model. This is one of the three compartmental model of Wollman and Reed in which total 131 I is considered to be one compartment and blood plasma is the other. The fraction rate constant for migration of 131I from plasma pool towards the reversible pool of the thyroid was effectively enhanced by PGF1α and PGF2α . The reversible fractional rate constant was variably affected. The fractional rate constant that regulates the interconversion of free iodide from labile pool to be oxidized is increased due to the action of PGF1α and decreased by PGF2α.