RNA transcription processes were visualized within chromatin from cultured Mouse cells, spread according to Miller, and Bakken (3), by high resolution autoradiography. The cells were labelled for a short time with 3H-uridine and lysed using the detergent Nonidet P 40. Transcription complexes of both ribosomal ("Christmas tree"-like forms) and non-ribosomal types were revealed and their structure is described.