Cavity ring-down spectroscopy was used to study the reaction of ClOO with NO in 50-150 Torr total pressure Of O-2/N-2 diluent at 205-243 K. A value of k(ClOO+NO) = (4.5 +/- 0.9) x 10(-11) cm(3) molecule(-1) s(-1) at 213 K was determined (quoted uncertainties are two standard deviations). The yield of NO2 in the ClOO + NO reaction was 0.18 +/-0.02 at 213 K and 0.15 +/- 0.02 at 223 K. An upper limit of k(ClOO+Cl-2) < 3.5 x 10(-14) cm(3) molecule(-1) s(-1) was established at 213 K. Results are discussed with respect to the atmospheric chemistry of ClOO and other peroxy radicals.