We have shown that following the in vivo administration of cyclosporin A (CsA) to either male or female Sprague-Dawley rats, there is a time- and dose-dependent inhibition of translation elongation in renal microsomes. Experiments reported in this paper explore the tissue specificity of translation inhibition. Following 6 days of oral 50 mg/kg/day CsA or control vehicle, animals were sacrificed and renal, hepatic and cardiac microsomal and cytoplasmic fractions prepared for “run-off” translation assays. These assays demonstrated that in vivo CsA resulted in a reduction in renal microsomal 3H- L-leucine incorporation to 25% of control values, a reduction of cardiac microsomal incorporation to 60% of controls and a stimulation of hepatic microsomal incorporation to 140% of controls. Cross-over experiments involving the addition of renal cytoplasmic fractions from CsA-treated animals to renal microsomal fractions from control-vehicle-treated animals depressed 3H- L-leucine incorporation to approximately 50% of control values. When the renal cytoplasmic fraction from CsA-treated animals was added to renal, hepatic or cardiac microsomal fractions from control-vehicle-treated animals, 3H- L-leucine incorporation values were consistently reduced to approximately 50% of controls. We have reported that translation elongation is inhibited by renal cytoplasm from CsA-treated rats in the presence of control renal cytoplasm. These data suggest that inhibition arises from the presence of an inhibitor rather than from a deficiency in elongation factors. The data reported in this paper demonstrate that microsomal fractions from various tissues have equal sensitivity to CsA-mediated renal cytoplasmic translation inhibition. These observations further suggest that renal translation inhibition is a result of more inhibitor being formed in, or taken up by, renal tissues than hepatic or cardiac tissues, and not due to a tissue-specific sensitivity to inhibitor. Renal translation inhibitor was also shown to inhibit eukaryotic translation in rabbit reticulocyte translation assays and prokaryotic translation in E. coli S30 coupled transcription/translation assays. The observation that translation elongation inhibition is most prominent in renal tissues, the site of dose-limiting CsA toxicity, suggests it may contribute to CsA nephrotoxicity.