Liquid scintillation counting ofp- cymene, derived from lemongrass oil, has provided information on the world-wide increase in C14 since 1954. By June 1959, the activity in the tropospheric atmosphere and in the rapidly equilibrating biosphere is measured to have increased by 26·8 per cent in the northern hemisphere and 19·7 per cent in the southern hemisphere. The shape of the relationship between activity and time is essentially linear, with two sections of quite different slope.