Abstract: A method of determining the concentration of pancreatic .alpha.-amylase and salivary .alpha.-amylase in a body fluid containing a mixture of said .alpha.-amylases. First and second samples of said body fluid are prepared, and the second samples are treated with an effective amount of an inhibitor capable of selectively inhibiting the activity of said .alpha.-amylases. The amount of total .alpha.-amylase, i.e. the sum of salivary .alpha.-amylase and pancreatic .alpha.-amylase, is then measured for said first and second samples, and the concentration of salivary and pancreatic .alpha.-amylase present in said first and second samples is determined by comparing the measured total .alpha.-amylase values with a standard. The inhibitor used has a discrimination factor--expressed as the ratio between the quantity of inhibitor necessary for reducing the activity of one of said two .alpha.-amylases by 50% and the quantity of inhibitor necessary for reducing the same activity of the other of said .alpha.