A variant immunoblotting procedure is presented, starting from sodium dodecyl sulfate-containing ultra-thin microgels. The use of these gels allows efficient transfer of proteins to an immobilizing matrix such as nitrocellulose, by simple uni-directional diffusion, without loss of resolution. To this end an assembly was developed, keeping the microgel and the immobilizing matrix in continuous contact. To standardize the technique, two protein extracts (a classical rabbit thymus extract and an original autologous nuclear extract) were used, together with reference antinuclear antisera. The method is fast, easy to perform, and perfectly reproducible. For these reasons, the technique is very suitable for screening a patient's sera on a large scale.