AbstractThe environment and the circumstances leading to the Sephadex group of products for gel filtration (SEC, size exclusion chromatography) are described. The importance of Porath's and the author's experience from zone electrophoresis is stressed. To be able to get high resolution the technique for packing columns was of decisive importance for electrophoresis. It paved the way for the observation of the separation properties of dextran gels. The synthesis of dextran‐based gels at AB Pharmacia and the development of varieties of them for varying applications are described together with the project leading to their marketing in 1959. The work of the author on gel filtration is summarized. The story is based on publication and memory. Aids to the latter have been laboratory notebooks and other documents still in the possession of the author.