Precursors of many secreted and cell surface proteins contain NH2-terminal signal sequences that lead proteins into the endoplasmic reticulum and to the cell surface. Methods have been developed to clone and identify such proteins by trapping their NH2-terminal signal sequences, so called signal sequence traps. In this study we present an alternative and simplified signal sequence trap based on the combination of a novel vector construct expressing a cDNA library in fusion with a CD19 reporter gene, transfection in mammalian cells and selection of cells expressing trapped signal sequences using magnetic beads. Using this method we have isolated several known and novel factors with signal peptides.