The infrared spectrum of the AsD radical in the X 3Σ − ground state has been recorded using CO laser magnetic resonance. The radical was formed by the reaction between D atoms and arsenic powder. Low- N transitions in the fundamental band and in the (2–1) and (3–2) hot bands have been detected. Hyperfine structure from the 75As nucleus ( I = 3/2) is seen on many of the resonances. These measurements have been combined with information from previous measurements of rotational transitions at sub-millimeter wavelengths [H. Fujiwara, K. Kobayashi, H. Ozeki, S. Saito, A.I. Jaman, J. Chem. Soc. Faraday Trans. 93 (1997) 1045–1051] to determine an extended and improved set of molecular parameters for 75AsD. Comparison is made with corresponding parameter values for AsH.