• The multiple allergosorbent test system (MAST) is a method for measuring total and allergen-specific IgE levels, using autoradiography and densitometry. The purpose of this study was to compare the results of MAST tests with those of radioallergosorbent (RAST) and skin tests as an adjunct to the diagnosis of allergy in children. Twenty children, aged 4 to 19 years, were studied. Total serum IgE level measured by the paper radioimmunosorbent test (PRIST) method ranged from 7 to 1,333 units/mL (geometric mean, 155 units/mL). Total serum IgE level by MAST significantly correlated with the PRIST IgE level. Quantities of allergen-specific IgE measured by MAST and RAST were also significantly correlated. When the diagnostic levels by MAST and RAST were compared with skin test reactions for ragweed, grass, house dust, and mite, MAST had a sensitivity of 59%, a specificity of 97%, and an efficiency of 72%, compared with 67%, 97%, and 78%, respectively, for the RAST analysis. We conclude that MAST and RAST are similar in their ability to measure allergen-specific IgE level, but that neither method is as sensitive as skin tests for detection of allergen-specific IgE.