The 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 stimulated with specific allergen in the presence of interleukin 3.23 patients allergic to Dermatophagoides pteronyssinus were included in this study. All subjects received no medication 2 weeks before the testing. Leukocytes were isolated by dextran sedimentation. After incubation with allergen the cells were centrifuged and the concentration of sulfidoleukotrienes in supernatant was determined. The results were expressed in pg/ml after subtracting the 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 3440 pg/ml. The mean level in the whole group was 1521.3 pg/ml at the optimal allergen concentration. Positive results were observed in 21 subjects. In 2 subjects we could not demonstrate leukotriene secretion by stimulation with allergen. 15 healthy control subjects were also included in this study. 12 subjects had negative skin prick tests (SPT) as well as CAST results. In 2 healthy subjects with positive SPT, we also observed positive CAST results. However, leukotriene secretion was lower than 300 pg/ml in these subjects. We conclude that CAST-ELISA is a valuable method for determining the allergic status in patients with mite allergy.