Polysaccharides that have been previously treated with reactive dyestuffs can be separated within 1 to 3 minutes by electrophoresis on PhoroSlides at potential gradients of 40 to 56 V cm–1. In addition to providing the required self-indicating system, dyeing increases the electrophoretic mobility of charged polysaccharides. The difficulty experienced in dyeing polysaccharides that have small proportions of primary hydroxyl groups (e.g., plant gums, pectin, alginic acid and sulphated polysaccharides) can be overcome by increasing the amount of sodium carbonate added in the dyeing process.