We have used a highly sensitive immunological tissue print technique to study cell- and tissue-specific expression of heterologous genes in transgenic plants. Primary polyclonal antibodies, raised against legumin of faba bean (Vicia faba L.) and 12S globulin of oat (Avena sativa L.) were used to localize these proteins in transgenic tobacco seeds in a streptavidin-alkaline phosphatase assay in combination with biotinylated secondary antibodies producing a higher sensitivity (by several amplification steps) of the assay. Both storage protein genes were found to be expressed in a specific pattern. While legumin is preferentially accumulated in certain parts of the embryo, the oat legumin-type globulin is restricted to the endosperm. The applied technique is highly sensitive with a resolution power down to the single-cell level and allows rapid screening of large numbers of samples.