Based on an analysis of robbery methods, the new security initiatives included an upgraded screen for behind-the-counter post office employees and staff training designed to enhance employee security sensitivity and performance. To determine the impact of these measures, the evaluation obtained data on every robbery incident within London sub-post offices for January 1, 1979 to March 31, 1986. Included in the data were raids on post office vans delivering money and other valuables to sub-post offices. There was a distinct decline in robbery levels beginning with the new security initiatives. The conclusion that the security measures contributed to this decline is based on the assumption that there would have been no further growth in robbery rates from the observed peak even without the new security measures. The evaluation thus probably underestimates rather than overestimates the impact of the security measures. 7 figures. 4 tables.