The effects of 4 buffers at different pH and of different molarities was tested on the immunoelectrophoresis of representatives of three serotypes and their natural mixtures of red clover necrotic mosaic virus (RCNMV). No substantial differences were observed with buffers at pH 7.2, 8.0 and 8.6. The representatives of the three RCNMV serotypes showed different mobilities in 0.1 and 0.01 mol/l ionic buffers in the agarose gel from cathode to anode. In nonionic 0.01-0.1 mol/l N-2-hydroxyethylpiperazine-N'-ethanesulphonic acid (HEPES) buffer, the RCNMV isolates moved from the anode to the cathode. Isolate TpM48 (serotype B) moved the most rapidly, while isolates No. 6 (serotype C) and TpM34 (serotype A) showed lower mobilities distinct from one another. This made possible a reliable differentiation of serotype B from serotypes A and C as well as of serotype A from serotype C. Agarose gels in 0.001 mol/l buffers proved to be unsuitable for the immunoelectrophoresis of RCNMV.