An earthen digester was constructed to treat the separated liquids from flushed dairy cattle manure. A floating cover was used to harvest the biogas produced. Satisfactory digester performance was found for both winter and summer conditions. However, biogas production was found to fluctuate seasonally with reduced biogas production being noted during the winter. Mean methane (CH4) yield was found to be 0·39 m3 CH4/kg volatile solids (VS) added. Mean biogas concentrations was 68·9% CH4 and 28·3% carbon dioxide (CO2). The loading rate during the period of study (31 October 1988–25 March 1991) was 0·12 kg VS/m3 -day.