This antibody has been developed especially for gel immunoprecipitation. The specificity has been ascertained by crossed immunoelectrophoresis using 12.5 microlitre antibody per square cm gel area against 2 microlitre human plasma. Thus, the specificity control is performed at an antibody concentration more than 16 times higher than the concentration generally used for rocket immunoelectrophoresis and single radial immunodiffusion.