The first observation is reported of laser oscillation in pure rotational transitions of the OH and OD free radicals. 44 lines in OH and 17 lines in OD have been seen in the 12‐ to 20‐&mgr; region. Transitions were observed within thev=0, 1, 2 vibrational levels of OH and thev=0 vibrational level of OD. Accurate values are calculated for theBandDrotational constants for OD and higher‐order rotational constants for OH.