Abstract: Methods of isolating antibodies by precipitation are disclosed. Various precipitants that can be employed in the invention are also disclosed, with PEG being a preferred precipitant. In a representative embodiment of the invention, the pH of a solution comprising an antibody of interest is adjusted to ±0.5 pH unit of the pI of the antibody, a precipitant such as PEG is added and the antibody of interest is subsequently isolated from the resulting precipitate. The antibody can be further purified if desired or it can be resuspended in a buffer. The invention can be employed as an alternative to or in addition to chromatographic isolation methods, such as methods that employ affinity chromatography.