Aspirin-induced asthma (AIA) is a clinical syndrome related to cysteinyl leukotriene overproduction in airways. The confirmation of the diagnosis requires inconvenient provocation tests with acetyl salicylic acid (ASA). A study was performed to evaluate whether measurement in vitro of cysteinyl leukotrienes (cys-LTs) release by isolated peripheral blood leucocytes, stimulated with ASA, can be of use for diagnosis of AIA. A cellular allergen stimulation test, CAST, was adapted to measure leukotriene release from leucocytes of 32 aspirin-tolerant and 26 aspirin-intolerant asthmatics. The cells were stimulated with Lys-ASA, N-formyl-methionyl-leucyl-phenylalanine (fMLP), or both fMLP and Lys-ASA, in a buffer containing IL-3, and results compared with human leukaemia cell line (Hl-60) response to Lys-ASA. Cys-LTs were measured in cell supernatant fluids by ELISA. ASA had a rather week stimulatory effect on cys-LTs release in both groups of patients. Contrary to some previous studies, no significant differences were found between cys-LTs release by leucocytes from AIA and ATA, or by differentiated Hl-60 cells. Measurement of cysteinyl-leukotriene release by peripheral blood leucocytes pre-treated with aspirin has no value for diagnosis of AIA.