The biogas production and some biochemical parameters of anaerobic fermentation at 30 degreesC for 40 days were studied for eight experimental groups of fermentation media, as affected by two factors: (I) the type of the animal waste (sheep waste, S and goat waste, G), and (2) the ratio of waste to olive cake which constitutes four levels (100:0 for S1 and G1; 80:20 for S2 and G2; 60:40 for S3 and G3 and 40:60 for 54 and G4). The results indicated that there was a significant decrease (P < 0.05) in the biogas production with an increase in the proportion of olive cake in place of animal waste. However, there was a significant increase in the biogas production for the S4 treatment compared with G4, reflecting an effect induced by the type of animal waste. The biogas production amounted to (1/kg VS/40 d): 62 (S1), 53 (S2), 49 (S3), 40 (S4), 58 (G1), 50 (G2), 44 (G3) and 25 (G4). The reduction in total solid (TS) weight, volatile solids (VS), neutral-detergent fiber decreased significantly (P < 0.05) with the increase in olive cake proportion in the digester. The reductions in VS were (% in DM): 58.2 (S1), 37.8 (52), 26.6 (53), 22.6 (54), 58.1 (G1), 36 (G2), 33.4 (G3), 14.4 (G4). The rates of energy consumption were (MJ/kg DM/40 d): 15.36 (S1), 10.12 (52), 7.84 (53), 6.68 (54), 14.16 (G1), 9.68 (G2), 8.41 (G3), 3.29 (G4). (C) 2001 Elsevier Science Ltd. All rights reserved.