The slowing-down spectrum in a CANDU-type reactor cell has been studied using resonance activation techniques. The measurements covered the energy range 1.46 ev to 367 ev. The effects of replacing the heavy water coolant with mixtures of light and heavy water and light water were studied. Measurements were also made in a channel without fuel clusters.The spectra observed in the normal cell were approximately 1/Ethroughout the cell except for depressions caused by prominent U238resonances. With no fuel in the cell, large departures from 1/Ewere observed.