Pistia stratiotes, an aquatic weed, was investigated as a substrate for biogas production. Experhnents were carried out as batch runs in laboratory-scale digesters with the addition of inoculum (digested cattle manure). Gas viehls were in the range of 533-707 litres kg-1 VS (STP), respectively, 21-28 litres kg- 1 fresh weight of P. stratiotes, with 30 days digestion time at temperatures of 29"5, 33"0 and 37"5°C. The average methane content was 58-68%. Due to its kigh biodegradability (approximately 83-99% of VS) Pistia stratiotes is veo' suitable as a substrate for biogas production.