Fast-food restaurants generate grease-containing wastewaters for which there is, currently no acceptable treatment technology The development of microbial cultures for use in a bioreactor could, therefore, provide effective treatment of these wastewaters. Thus, the growth of a range of pure and mixed cultures was examined using vegetable oils, lard and 'grease' from a fast-food restaurant grease-trap. The pure cultures were Acinetobacter sp., Rhodococcus rubra, Nocardia amarae and Microthrix parvicella and these were compared with a mixed culture isolated from a grease-trap, MC1, and with activated sludge. The effectiveness of these cultures was assessed in terms of their grease-removal efficiency the biomass production and yield coefficients. Acinetobacter was the most effective of the pure cultures, typically removing 60-65% of the fatty material whose initial concentration had been 8 g/l. The effectiveness of the mixed culture, MC1, was variable, with the removal efficiency ranging from 29% for rapeseed oil to 73% for the restaurant grease. The activated sludge gave a more consistent removal, which was generally better than 90%. However there was a lag phase of about I day in every case. Acclimatised activated-sludge did not exhibit a lag phase and also achieved a high (>90%) removal efficiency. The absence of a lag phase resulted in faster growth and fat removal. (C) 1997 Elsevier Science Ltd.