13C and 14C were measured in the upper Jordan River, in its tributaries which issue from the Mount Hermon aquifer, and in the local atmospheric CO2 to evaluate the degree to which changes in the atmospheric 14C levels influence the 14C levels in the aquifer and in the Jordan River. The exchange fraction of CO2 between the river and the atmosphere was calculated for fall 1983 with the two carbon isotopes and it is shown that the value obtained with 14C (0.364) is the more reliable. The ratio of 14C in the Jordan River to that in the atmosphere in 1972 is similar to that in 1983, 0.66 and 0.67, respectively. This implies an approximately constant ratio (0.44) between the 14C level in the Mount Hermon aquifer baseflow and the 14C level in the atmospheric CO2. This information can be combined with the known historical fluctuations in the 14C levels of the atmosphere to calculate the 14C fluctuations in the discharge of the Jordan River into Lake Kinneret, backwards in time.