Aldosterone increased methylation by [methyl-3H]methionine of nuclear rRNA sedimenting at 18S, 28S and 40S within 90 min and of 28S cytoplasmic RNA within 240 min of continuous exposure to the precursor and the hormone, in the toad [Bufo marinus] bladder. Incorporation of [14C]uridine into cytoplasmic 4S tRNA and 18S and 28S rRNA was enhanced after 240 min of continuous exposure to the precursor and the hormone. Aldosterone had minimal effects on the 3H or 14C-labeled, acid-soluble pools. Aldosterone probably augments the synthesis of rRNA at the transcriptional level. Ribosomes isolated 240 min after treatment of the toad bladder with aldosterone showed increased incorporation of [3H]-phenylalanine into peptides with both endogenous mRNA and exogenous mRNA, i.e., poly(uridylic acid), in an in vitro assay. Inhibition of reinitiation with NaF or poly(AUG) reduced the rate of amino acid polymerization by 45%, but the aldosterone to control ratio remained significantly high. An increase in active ribosomes and perhaps in endogenous mRNA content is implied. These findings do not distinguish between a steroid-dependent increase in the total number of active ribosomes and an increase in translation activity per ribosome.