Abstract: A medium for isoelectric focusing is produced which consists of or contains agarose into which positively charged substituents have been introduced to neutralize negatively charged groups inherently present in the agarose, said substituents containing as the only charged group a quaternary amino group with a positive charge independent of pH at least in the range 2-12. The medium may consist of a mixture of two or more agarose preparations with different degrees of substitution with regard to the introduced substituents. Unmodified agarose may also constitute one of the components of the medium.