1. The turnover of RNA in various subcellular fractions of normal and adrenalectomized female rats was measured by injection of a single dose of [14C]orotic acid and then following the loss of radioactivity from nuclei, mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, free polysomes, total ribosomes and low molecular weight RNA.2. The half-lives (t12) for the above fractions from normal rats were 7.41, 5.85, 5.13, 5.03, 5.47, 4.11 and 4.60 days, respectively. The t12 values for adrenalectomized rats were 9.23, 7.32, 6.11, 6.03, 5.81, 6.03 and 4.93 days, respectively.3. The slower turnover rate in adrenalectomized rats suggests a slower rate of RNA synthesis (steady state approximation). This is consistent with the lowered activities of RNA polymerases I and II observed in our previous study (Mishra, R. K., Wheldrake, J. F. and Feltham, L. A. W. (1972) FEBS Lett. 24, 106).