1121. More on environmental radioactivity: Ellis, R. E. (1965). An appraisal of the current fall-out levels and their biological significance. Physics Med. Biol. 10, 153. Mayneord, W. V. (1965). Mans' natural radiation environment. In Radioaktive Isotope in Klinik und Forschung, Vol. VI. Proceedings of International Symposium at Bad Gastein, Austria, in January 1964. Urban & Schwarzenberg, Munich—Berlin, 1965