In 5 experiments, single or regular addition of liquid polyphosphates (N 10%, P2O5 34%) at up to 4 ml/l to liquid dairy cattle or pig manure (TS 5-7%) did not reduce odour, COD or pH. Single or regular addition of potassium permanganate at 300 p.p.m. or a pesticide wetting agent at 0.26 or 0.13 ml/l reduced the odour of pig manure but neither these nor regular addition of a nitrogen/Zn fertilizer (N15%, Zn 5%) at 2 ml/l had any affect on the odour of dairy manure. Addition of potassium permanganate 300 p.p.m. or a combination of polyphosphate at 2 ml and N/Zn fertilizer at 2 ml/l reduced the COD of pig manure. Liquid polyphosphate fertilizer solution, potassium permanganate, a pesticide-wetting agent, nitrogen-zinc liquid fertilizer solution and a digestive deodorant were used to treat liquid dairy and swine manure to control odours. Treated samples were evaluated by a panel for odour strength and quality. The polyphosphates did not control odours in manure when added shortly after spreading or reduce them significantly when added at regular intervals. Potassium permanganate at concentrations of 300-500 ppm was the most effective compound tested. The pesticide wetting agent also reduced odours.