The rate constant for the gas-phase reaction of isopropyl peroxy radicals with NO has been measured over the temperature range of 201-401 K using chemical ionization mass spectrometric detection of the peroxy radical. The temperature dependent expression for the rate constant was found to be k(T) (2.7 +/- 0.5) x 10(-12) exp{(360 +/- 60)/T} cm(3) molecule(-1) s(-1) which gives a rate constant of k = (9.0 +/- 1.5) x 10(-12) cm(3) molecule(-1) s(-1) at 298 K. This value is a factor 1.8-2.6 higher than previous measurements.