The RIDS (rugosity-insensitive density system), a gamma-gamma system that can operate in very rough boreholes by virtue of special sensors that make contact with the walls of the hole, has been tested over a density range of 0.6 to 2.6 g per cu cm in the field. Error is believed to be less than + or - 2.5 percent over much of the range. Tight collimation and energy discrimination limit detection to singly Compton-scattered gamma energy. Substantial errors in density measurements can occur in other logging systems, in particular where the hole is rough enough to cause gaps between the sonde and the wall; such errors can range from 4 to 25 percent for only a 1-cm gap between sonde and wall. RIDS results agree within a few percent with those of other logging systems where the latter are not perturbed by gaps between sonde and wall, and with core data when available.