Standardized immunoassays for environmental monitoring require monoclonal antibodies (MAbs) with defined selectivities and affinities. An important step in the production of MAbs is the development of efficient screening procedures to identify suitable cell lines. We demonstrate the usefulness of immunomagnetic cell separation for the screening of hybridomas. It is based on the expression of surface receptors resembling the secreted antibodies on the membrane surface of hybridoma cells. Producers are tagged by the target molecule covalently linked to magnetic beads and subsequently removed by permanent magnet. Several examples are given surpassing conventional techniques for the screening of s‐triazine antibodies.