The effects of quinacrine, an antimetabolite which intercalates into DNA, on the ultrastructure of interphase nuclei and on RNA turnover were studied in primary cultures of rat hepatocytes. Procedures included ultrastructural cytochemical staining for ribonucleoprotein and DNA, autoradiography, and measurement of labeled uridine uptake and incorporation. Addition to the culture medium of a nontoxic dose (10 microM for 30 min) reduces the net accumulation of labeled uridine in RNA. This involves first heterogeneous RNA and then ribosomal RNA since their structural precursors, interchromatin fibrils and nucleolar fibrils, respectively, diminish in that order. Intranucleolar chromatin retracts, and perinucleolar chromatin becomes unusually condensed. A toxic dose (50 microM for 30 min) produces greater inhibition of tritiated uridine incorporation in RNA. This precedes and is not due to a drop in uridine uptake into the cells. Toxic doses produce unusually large clusters of interchromatin granules which are embedded in an unusual dense material which stains positively for ribonucleoprotein. Three regions of the chromatin are altered. (a) Perinuclear condensed chromatin retracts from the nuclear envelope, remaining attached by short DNA-containing bridges. (b) The normally dispersed nucleoplasmic chromatin condenses into a stainable network which retracts centrifugally. (c) Perinucleolar chromatin becomes a network of small highly condensed masses or bands interconnected by fibrils which are either decondensed or stretched. These alterations in chromatin structure probably form the basis of quinacrine-impaired nuclear metabolism.