Cross-linkage of FcεRI on human lung mast cells purified by affinity magnetic selection with monoclonal antibody YB5.B8 against c-kit (purity > 90%) expressed mRNA for multiple cytokines. There was no constitutive expression of interleukin (IL)-4 mRNA. Mast cell stimulation with anti-IgE induced IL-4 mRNA expression which appeared maxmal at 2 h and waned slowly over the next 24 h. IL-5, IL-6, IL-8 and tumour necrosis factor (TNF)-α mRNA were constitutively expressed. Mast cell activation with anti-IgE led to an increase of IL-5 and TNF-α m RN A signals within 2 h and which persisted for at least 24–48 h. On the other hand, IL-6 and IL-8 mRNA expression were not affected by anti-IgE challenge.