The report gives results of 4-month-long alpha-track detector (ATD) measurements of indoor radon concentrations, completed during the winter of 1988-89 in 38 of 40 houses where radon reduction techniques had been installed 2-4 years previously during an earlier EPA project. The techniques, installed between June 1985 and June 1987, generally involved some form of active soil ventilation: three were air-to-air heat exchangers, and two involved carbon filters to remove radon from well water. The purpose of these measurements was to determine if the radon reduction performance of the systems had degraded compared to previous wintertime radon measurements. Comparison of the current ATD results with those from 1986-87 and 1987-88 indicates that, in the 34 houses where the system was in continuous operation during this measurement period, the radon levels generally compared well with those measured during the previous years. In only two houses did significant, unexplainable increases occur. Two soil ventilation fans failed during the previous year: 5 out of 34 fans have failed to date. One air-to-air heat exchanger has needed repair. The one water treatment unit designed specifically for radon removal is giving 97% removal, whereas the other has degraded to 65%.