Abstract The fundamental vibration-rotation band of the 79BrO and 81BrO radicals in the 2Π 3 2 ground electronic state was observed in the region 700–760 cm −1 by using a Zeeman-modulated infrared diode laser spectrometer. The BrO radical was generated directly in a multiple reflection Zeeman cell by a 60-Hz discharge in a mixture of Br 2 and O 2. The observed absorption lines, 20 and 22 in number for 79BrO and 81BrO, rspectively, were combined with the microwave data of Cohen et al. [ J. Mol. Spectrosc. 87, 459–470 (1981)] and were subjected to least-squares analysis to determine the rotational and centrifugal distortion constants for both the v = 0 and v = 1 states and also the band origin. The band origin obtained for 81BrO, 721.92814(57) cm −1, gives a support to the value 714 (10) cm −1 estimated by Cohen et al. using the microwave data and also the result 722.1 ± 1.1 cm −1 obtained by Barnett et al. [ Canad. J. Phys. 59, 1908–1916 (1981)] from a reanalysis of the A 2Π i - X 2Π i absorption spectrum.