The electrochemical reactions of lithium with MnSb (NiAs-type structure) and Mn2Sb (Cu2Sb-type structure) have been investigated by in situ X-ray diffraction. Lithiation of MnSb proceeds via an intermediate LiMnSb structure before transforming, with Mn extrusion, to Li3Sb. The reaction is reversible. On delithiation, the X-ray data show solid-solution behavior between Li3Sb and LiMnSb, which is facilitated by the strong structural relationship between these two compounds. MnSb electrodes deliver a rechargeable capacity of 330 mAh/g when cycled between 1.5 and 0 V vs. metallic lithium. By contrast, the initial reaction of Mn2Sb with lithium proceeds almost directly to Li3Sb with little LiMnSb formation. Thereafter, Mn2Sb electrodes behave in an almost identical manner to MnSb electrodes, but deliver a rechargeable capacity of less than 300 mAh/g because of the surplus Mn in the electrode. The electrochemical and structural properties of MnSb and Mn2Sb are compared with the structurally related compounds Cu6Sn5 (NiAs-type structure) and Cu2Sb, respectively.