A recently developed CAST-ELISA method was applied to determine allergen-induced leukocyte stimulation. This method is based on the measurement of sulfidoleukotriene secretion by peripheral blood leukocytes previously stimulated with specific allergen in the presence of interleukin 3. 24 patients allergic to different aeroallergens and some food allergens were included in this study. Subjects received no medication 2 weeks before the testing. Leukocytes were isolated by dextran sedimentation. After incubation with allergen at two concentrations, the cells were centrifuged and the concentration of sulfidoleukotrienes in supernatant was determined. The results were expressed in pg/ml after subtraction of values of spontaneous sulfidoleukotriene production in portions incubated without allergen. We observed a wide range of sulfidoleukotriene secretion upon allergen stimulation. Concentrations of leukotrienes ranged from 0 to 5780 pg/ml at lower allergen concentration and from 210 to 5680 at higher allergen concentration. On the basis of observed results, we conclude that the better allergen concentration is the higher one because there was no appearance of negative cell stimulation. In the lower allergen concentration we observed negative results in two cases. Sixteen healthy control subjects were also included in this study. Eleven subjects had negative skin prick tests (SPT) as well as CAST results. In 5 healthy subjects with positive SPT, we also observed positive CAST results in 4 persons. In 1 healthy person with positive SPT results, CAST results were negative. We conclude that TOP-CAST allergen is a valuable mixture of different aero and food allergens for determining the allergic status in patients with suspicious allergic status, although it cannot differentiate between health and disease states.