1. 1. Interactions of various polyanions with histones and the resulting effect of the DNA-dependent synthesis of RNA in vitro was investigated. None of the studied polyanions, nuclear acidic protein fractions from liver or thymus, RNA, polyribonucleotides and polyamino acids, were able to reverse the histone inhibition of RNA synthesis once the histone-DNA complex was established. 2. 2. However, the acidic nuclear proteins and poly amino acids, but not the RNA or polyribonucleotides, would prevent much of the histone inhibition of RNA synthesis in vitro if interacted directly with histones prior to their association with DNA. 3. 3. The failure of RNA and polyribonucleotides to reverse the inhibition of RNA synthesis in vitro by histones is due to the dissociation of RNA-histone complexes by the template DNA used in the RNA polymerase assay mixtures. A simple technique to measure histone-RNA-DNA complexes on millipore filters is described. © 1969.