Bronchoalveolar lavage cells and bronchial biopsies were obtained from nine patients with red cedar asthma, six atopic asthmatics and six non-atopic, non-asthmatic control subjects. There were similar proportions of neutrophils, mast cells, lymphocytes, and macrophages in BAL samples from all three groups, but eosinophil numbers were elevated in patients with cedar asthma and atopic asthma (3.0 and 2.5% respectively versus 0.5% in control subjects; p < 0.05 for each group). In bronchial mucosal biopsies, mean numbers of T cells were elevated in both asthmatic groups (cedar asthma 9.8 times, and atopic asthma 2.6 times, control values). CD4+ cells accounted for most of the increase in T-cell numbers, while CD8+ cell numbers were elevated in biopsies from a minority of cedar asthma patients. Absolute numbers of CD25+ (IL-2 receptor-bearing) cells were increased in cedar asthma but the proportion of T cells expressing CD25, was similar in all three groups. Activated eosinophils (EG2+) were increased in both asthmatic groups, with mean numbers 2.5 times greater in the cedar asthma biopsies than in atopic asthmatics. Thus both cedar asthma and atopic asthma are associated with increased numbers of T-cells and activated eosinophils in the bronchial mucosa. There was no major histologic difference between atopic asthma and red cedar asthma.