Attacks of fatal asthma have been shown to be either of short duration or long duration and associated with differing degrees of smooth muscle contraction, luminal mucus deposition and ratios of eosinophils to neutrophils in the airway wall. We hypothesized that this bimodal distribution might be related to airway mast cell degranulation.Methods: Airway sections from cases of fatal asthma in the second Victorian asthma mortality study and from cases coming to coronial autopsy in Perth were examined. Tryptase-positive mast cells, numbers of intact and degranulated mast cells, post-mortem blood salbutamol levels and airway dimensions were measured.Results: Although the total number of mast cells were similar, the ratio of degranulated to intact mast cells (D/I) was significantly increased in the smooth muscle (P <0.05) and outer airway wall (P <0.001), in short-duration cases compared with long-duration cases. Proportional muscle shortening was significantly increased (P <0.05) in short-duration cases (17 ± 7%) compared with long-duration cases (11 ± 7%). Blood salbutamol levels were related to the total airway wall mast cell D/I ratio for all cases combined (r = 0.57, P = 0.01).