Two forms of yeast RNA polymerase A are resolved by phosphocellulose chromatography. One of these, called RNA polymerase A, is lacking two polypeptide chains of 48,000 and 37,000 daltons. The properties of the two enzymes are compared in the present paper. RNA polymerase A transcribes d(A-T)n with a similar efficiency as the complete enzyme, but it is comparatively much less active with native DNA. The two enzymes can also be differentiated on the basis of their ionic strength and divalent cation requirements. RNA polymerase A has a particularly low activity at high salt and low Mg2+ concentrations. Thermal inactivation curves of the two enzymes are different when residual activity is assayed with native DNA. In contrast with d(A-T)n as template the apparent inactivation curves of the two enzymes are identical. The data suggest that the two dissociable polypeptide chains play an important role in transcription. The template specificity of yeast RNA polymerase B was further investigated using SV40 DNA-FI as template. RNA polymerase B is able to retain [3H]SV40 DNA-FI on nitrocellulose filters but the enzyme-DNA complex is very unstable. The observation that RNA polymerase B can transcribe to some extent a supercoiled DNA but not a linear double stranded template supports the hypothesis that the enzyme needs some unpaired DNA structure to initiate transcription.