['Marked variations in the interleukin-4 (IL-4)-producing capacity of basophils can be observed when aliquots from the same cell preparation are kept under different conditions before stimulation. The aim of this study was to identify factors affecting the functional activity of basophils and to determine optimal storage conditions.', 'Healthy blood donors.', 'Aliquots of purified basophils were kept for different time intervals on ice or at 37 degrees C, in buffer or culture medium, respectively. Following subsequent stimulation with anti-IgE, IL-4 release was determined.', 'Upon storage times up to 4 h, basophils produced more IL-4 when kept at 37 degrees C as compared to 4 degrees C. Surprisingly, buffer was superior compared to culture medium for storage. When the storage time was 20 h, IL-4 release was reduced significantly under all conditions studied.'] Is interleukin-4 production from human basophils critically dependent on the storage conditions employed prior to stimulation?