The attitude of phosphohexoseisomerase (PHI), a glycolytic enzyme, in parotid and submandibular saliva of healthy human control subjects of different sex and age was studied flow rate dependent. The results obtained from this group were compared to the PHI activity measured in the saliva of patients suffering from salivary gland diseases. Significantly elevated salivary PHI levels were found in chronic sialadenitis, while in sialadenosis, parotid gland infarction and parotid cysts the enzyme activity was within the normal range. Single patients suffering from parotid gland tumors showed elevated PHI values. A possible role of salivary PHI activity for the differential diagnosis of salivary gland diseases is discussed.