A prototype on-line reactivity meter using reactor noise analysis techniques is based on a two-detector cross correlation method, which offers as a special feature the absence of uncorrected noise contribution to the spectral density function of the reactor system. Reactivity shutdown measurements were performed on three different zero power reactors down to seven dollars. Special attention is given to the predicted and measured error margins of reactivity. The described on-line meter, when used with optimized current type neutron detectors for minimum gamma contamination, promises to be an encouraging way of making shutdown reactivity measurements, perhaps also in “dirty” power reactors where the high gamma-ray intensities can considerably destroy the “clean neutron signal-to-noise” ratio.