A method has been developed for the measurement of soil water diffusivity. The method is based on gamma ray absorption measurements of the water content as a function of time at a fixed position in a horizontal infiltration system. The calculation of diffusivity is based on the assumption that the water content is a function of position divided by the square root of time. The variability of the data led to scatter in the diffusivity function especially at high water contents. This variability in the data can be traced mainly to the inability to obtain sufficiently accurate data from the recordings of the gamma ray counting system. When the diffusivity function thus obtained was used to predict the water content time relationship in the column, even though the function had been fit statistically, the results were largely dependent upon the wet end of the relationship.