In this study the changes in water content in the unsaturated zone of a large esker at Tärnsjö have been measured with a combined gamma/neutron probe. Periods of heavy rainfall and intense snow-melting have resulted in infiltration events, which later have been traced as zones with high water content moving downwards in the unsaturated zone towards the groundwater table. The results indicate a velocity of the movement of such zones of about 1.5-3.0 m/month. These results are compared with those obtained by Andersen and Sevel (1974) from a study in Denmark, and with preliminary results from a study of the movement of tritiated water in the unsaturated zone of the Tärnsjö esker performed by Z. Dressie.