A method is described for labeling proteins with 7.2 h half-life 211 At. The alpha particle-emitting nuclide was coupled to goat IgG using an N-succinimidyl 3-(tri-n-butylstannyl) benzoate intermediate. The reaction and purification sequence requires about 2 h to produce 211 At-labeled IgG in 25-40% radiochemical yield. Comparative blood clearance measurements in mice suggest that the 211 At-labeled IgG conjugate is stable in vivo.