B-N-Acetylhexosaminidase in human serum were studied by heat inactivation using spectrofluorometric method. This enzyme consist of two major forms

HEXA (heat labile) and HEXB (heat stable). Two hundred and seventy six serum samples from normal subjects (n=120), control subjects (n=49) and obstructive jaundice patients (n=107) were analysed. The values (mean(+or-) SD) of total HEX were 18.5 (+or-) 3.5 U/min, 20.8 (+or-) 5.6 U/min and 38.9 (+or-) 14.6 U/min respectively

HEXB were 6.3 (+or-) 1.9 U/min, 9.0 (+or-) 3.8 U/min and 18.9 (+or-) 9.6 U/min respectively

and HEXA were 12.1 (+or-) 2.0 U/min, 11.8 (+or-) 3.7 U/min and 20.1 (+or-) 6.5 U/min respectively. The total HEX,HEXB and HEXA in obstructive jaundice patients compared to normal and control subjects were statistically significant increasing (P < 0.001). In according to tissue diagnosis, the benign (n=10) and malignant (n=25) biliary obstruction were determined. The results showed the increasing of total HEX,HEXB and HEXA in malignant biliary obstruction but no statistically significant increasing at P < 0.05. Increased level of HEX may defect in clearance HEX of the liver and over releasing from malignant cells. Seventeen fasting sera of obstructive janudice patients were studied the correlation between total HEX, HEXB and HEXA with total bile acids. The total HEX and HEXA were correlated to total bile acid (P < 0.05) with correlation coefficient (r) of 0.511 and 0.644 respectively. These are consistent with the idea that elevated bile acid in circulation can damage the Kupffer cell membranes, impeding the clearance of the HEX from the circulation resulting in elevated serum levels.