Voltage-gated potassium channels of plants are multimeric proteins built of four alpha-subunits. In the model plant Arabidopsis thaliana, nine genes coding for K(+) channel alpha-subunits have been identified. When co-expressed in heterologous expression systems, most of them display the ability to form heteromeric K(+) channels. Till now it was not clear whether plants use this potential of heteromerization to increase the functional diversity of potassium channels. Here, we designed an experimental approach employing different transgenic plant lines that allowed us to prove the existence of heteromeric K(+) channels in plants. The chosen strategy might also be useful for investigating the activity and function of other multimeric channel proteins like, for instance, cyclic-nucleotide gated channels, tandem-pore K(+) channels and glutamate receptor channels.