The report gives results of 12-month-long alpha-track detector (ATD) measurements of indoor radon concentrations, between December 1988 and December 1989 in th living areas of 38 of 40 houses where radon reduction techniques has been installed 2-4 years earlier in a previous EPA project. The techniques, installed between June 1985 and June 1987, generally involved active soil depressurization. In the 28 houses in which the mitigation system operated the entire year, the annual average was < 2 pCi/L in 13, and < 4 pCi/L in 22. The residual radon in many houses is due largely to re-entrainment of ASD exhaust. Comparison of these annual ATD results with quarterly results from the past three winters shows that 22 of the 28 houses had annual measurements within 1 pCi/L of the winter-quarter result. There had been no significant degradation in system performance, except where the mitigation fans failed or where the owner had turned off the system. Six of 34 ASD fans have failed to date.