A modification of radioimmunosorbent technique(RIST)was applied to the determination of IgE concentration in saliva for the diagnosis of allergic diseases in the clinic of oral surgery. A 1.0 ml of anti-IgE combined with Sephadex particles was mixed with a 0.1 ml of saliva and rotated vertically for 40-44 hours at room temperature. After this pre-incubation, 0.1 ml of ^<125>I-IgE solution was added and the mixture was vertically rotated again for 18-24 hours at room temperature. After the incubation, bound- and free-IgE were separated according to the manual of Phadebas IgE Test(Pharmacia). The data obtained by the above procedures were satisfactory in its accuracy, precision and sensitivity. It was capable of detecting 0.2-20 unit/ml. Using this method, IgE concentration in whole saliva obtained before rinsing out the mouth in the morning was determined on non-allergic Japanese adults, and most of the data were in the range of 0.13 to 5.70 unit/ml. It was further demonstrated that the method was applicable to the determination of IgE levels in low protein specimens such as urine or cord serum.