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Chitosan has been investigated as an inexpensive, biologically derived adsorbent and/or primary coagulant for two reactive azo dyes in textile wastewater. At natural pH, complete elimination of colour was achieved from 0.1 g/L aqueous solutions of the textile dyes Procion Orange MX-2R and Procion Red MX-5B with a dose of 6 g of chitosan per litre of dye solution. However, when pH was lowered (to 4.8 and 5.5 respectively), a dose of only 1 g of chitosan per litre was necessary to eliminate colour and drastically reduce TOC (total organic carbon) and chemical oxygen demand for the same concentration of dyes. This allowed about an 80% reduction in sludge volume production. Addition of sodium phosphate dibasic and potassium sulfate improved the dye removal at higher pH. Colour removal decreased significantly with or without added salts as pH was adjusted above 7. Equilibrium adsorption experiments showed that both dye solutions follow the Freundlich isotherm, but not the Langmuir isotherm. Kinetics measurements show a better fit to the pseudosecond-order Lagergren model than to the first-order Lagergren model. Brunauer-Emmett-Teller, or BET, surface area analysis and scanning electron microscope micrographs were included for better understanding of the nature of the chitosan surface with and without adsorbed dye. Chitosan appears to be a natural, clean and excellent product for the adsorption of Procion Orange MX-2R and Procion Red MX-5B in mildly acidic conditions.