[en] Computing soil moisture content with a neutron probe requires use of a calibration curve that considers the thermal neutron capture cross section of the hole liner, as well as the hole diameter. The influence of steel, polyvinyl chloride, and aluminum casings that fit 0.051- to 0.102-m hole diameters was determined by comparison with neutron probe readings in uncased holes of corresponding diameters. Eccentricity of probe location was considered a potentially significant variable. The experiment was run in disturbed Bandelier tuff with an average dry density of 1.35g . cm^-3 and moisture content of 3.8 to 26.7% by volume. The casing material and hole diameter influenced the probe readings significantly, whereas eccentric location of the probe did not. Regression analyses showed an almost perfect inverse linear correlation between hole diameter and count rate