The invention provides anovel approach for the suppression of endogenous antibody expression in non-human transgenic animals genetically engineered to express one or several human or humanized immunoglobulin transloci. Endogenous immunoglobulin expression in transgenic non-human animals is suppressed by selective expression of a suicide gene like a toxin only in B-cells expressing endogenous immunoglobulin but not in B-cells expressing human(ized) immunoglobulins. This method allows the dominant expression of transloci coding for humanized or human antibodies in the blood, milk and eggs of transgenic animals.