Radiochemically pure [¹⁸⁸ReX(CO)₅] (X = Cl, Br, and I) were prepared for the first time by high-pressure carbonylation of ¹⁸⁸ReO₄ ⁻ with carbon monoxide in an aqueous solution in the presence of halide ions at 210 °C. The complexes were isolated at the n.c.a. level from the reaction mixture by gas-phase transport with carbon monoxide at a high pressure. The procedure allows obtaining the target compounds in any appropriate solvent (aqueous and nonaqueous), which may open new synthetic prospects for the development of novel therapeutic radiopharmaceuticals.