Accurate initiation of transcription in vitro requires, in addition to RNA polymerase II, factors present in soluble extracts of cultured cells. We have developed transcription system in vitro, which permits us to visualize the transcription-initiation complexes on a mouse beta globin restricted fragment from a recombinant beta globin bacteriophage DNA. Using the lambda fragments as internal controls this system has allowed us to assess the specificity of transcription with RNA polymerase II. Comparing extracts from cells and tissues expressing the globin genes (Friend cells, spleen and blood from phenylhydrazine-induced anemic mice) with those which do not (thymus, liver, PCC3 cells), we observed that specific initiation of transcription on the beta globin gene occurs only with soluble extracts from erythroid tissues. This tissue-specific transcription is partially sensitive to alpha-amanitin and occurs at the 5' end of the globin gene.