SUMMARYInfiltration from ring infiltrometers of different radii was measured into four soil materials contained in laboratory tanks. The infiltration per unit area was larger the smaller the ring size, coming to a steady state at an earlier time. Scaling based on similar media theory was applied to the results using a microscopic characteristic length defined in terms of the hydraulic conductivity of the saturated soil and a macroscopic characteristic length taken as the radius of the ring. The relationships between scaled cumulative infiltration and scaled time merged into a single relationship at small scaled times for all soil materials and for all sizes of ring, but were different for the different soils and for the various ring radii at large scaled times. The relationship at small times was used as a type curve to interpretin situmeasurements with ring infiltrometers on three field soils in terms of the hydraulic conductivity of the saturated soil. These estimates of hydraulic conductivity pertained to the small volume of soil near the surface which was wetted during the measurement. Large variations in hydraulic conductivity values were found from experiments with small sized rings, but little variation was found for large sized rings. The technique provides a simple method of investigating soil structural changes near the surface.