The effect of a single administration of tryptophan on the transport of nuclear RNA to the cytoplasm of rat liver was investigated. Using a cell-free system containing nuclei (RNA labeled in vivo with [ 14C]orotate) and dialyzed cell sap of liver, the isolated hepatic nuclei of tryptophantreated rats demonstrated an increase in the release of labeled RNA into the medium in comparison to hepatic nuclei of control rats. Also, liver cell sap of tryptophan-treated rats with added tryptophan to the medium was found to stimulate the release of labeled RNA (poly(A)-mRNA) from isolated control nuclei. Pretreatment of rats with cycloheximide or puromycin before tryptophan administration prevented the liver cell sap effect. However, the hepatic nuclei of puromycin- and tryptophan-treated rats demonstrated an increase in the release of labeled RNA into the medium incubated with control liver sap, similar to that observed with hepatic nuclei of rats treated with tryptophan alone. These results suggest that the tryptophan-induced enhancement of nucleocytoplasmic translocation of RNA may be related to alterations in the controls within the nucleus and cytoplasm that act to regulate the intracellular transport of RNA.