Released T4 and T3 hormones in albino rat blood after an exogenous administration of PGB1, PG1α and PGF2α were determined and correlated with the serum content of calcium. Results revealed that all the tested PGs significantly raised the levels of T3 and T4 in rat serum, but not affect the serum calcium levels. PGB1 and PGF1α reduced the thyroidal calcium content due to enhancing the ellular permeability. However, the effect of PGF2α due to enhancing the lysosomal proteolytic enzyme activity.