The neutron monitoring experiments conducted at ZPPR successfully demonstrated the feasibility of using 3He proportional counters to measure the neutron field in a plutonium storage vault. During the experiments, count rate stability at the ±0.04 to ±0.05% level was maintained for extended periods of time. A removal sensitivity of about 1 kg of plutonium from a nominal vault inventory of 2500 kg was achieved. This sensitivity applies to removal from any storage cell in the vault and is based on 4000-s counting periods. Statistically, for this situation, we had predicted a false-alarm rate with a 1-kg trip level to result in one false alarm per 2 years of continuous monitoring. The 8-month vault monitoring experience at ZPPR indicates that, with only modest hardware improvements, this level can be achieved.