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Highly alkalitolerant and moderately thermotolerant Bacillus sp. NZ, isolated from degrading lignocellulose, produced a novel highly thermotolerant and alkalitolerant endoglucanase. Maximum activity of endoglucanase was observed in the medium with the initial pH= 9 (920 U/L) after 72 h of fermentation with shaking (250 rpm) at 45 C. Growth of the organism and enzyme production displayed a precise relationship, showing maxima after 72–96 h of fermentation; however, the organism formed maximum biomass at pH= 8, but produced the highest enzyme titre at pH= 9. Among the examined crude substrates, wheat bran gave maximum activity of endoglucanase (1960–2280 U/L), and was followed by wheat straw (1480–1760 U/L), filter paper (1360–1450 U/L) and sawdust (1160 U/L). Soybean meal served as a suitable nitrogen source for good production of endoglucanase. The enzyme showed activity over a broad pH range (5–10), with maximum at pH= 9–10 (2240–2290 U/L). Endoglucanase was highly active (2210–2300 U/L) over a broad range of temperature (50–100 C), with maximum activity at 50 C (2290 U/L) and at 90 C (2300 U/L). Significantly high activity was observed even at 100 C (91.3%). The enzyme was highly stable at temperatures from 60 to 90 C for a period of 30 min. Endoglucanase was purified 23-fold using ammonium sulphate precipitation. Substantial activity and stability of endoglucanase at elevated temperatures and at pH extremes indicate a potential for its successful application in industries.