Abstract The association between stress, humoral and cellular immune response and intestinal parasites was evaluated in 102 patients in a randomized double‐blind study. Sixty‐four (62.7 per cent) presented respiratory allergic disease (RAD) at the time of the clinical and laboratory tests; the other 38 (37.3 per cent) were normal individuals. Higher levels of IgE associated with RAD were observed in patients with family dysfunction ( p < 0.05). All the other immunological parameters that were measured — total B and T lymphocytes, helper (CD4) and suppressor/cytotoxic (CD8) T lymphocytes as well as IgG and IgA levels — were similar in both the allergic and the control groups. Twenty‐two patients (22.5 per cent) were positive for Giardia lamblia , 86.3 per cent of them suffering RAD ( p < 0.03). Regression analysis showed that patients with high levels of IgE and eosinophilia were associated with G. lamblia infection. This study indicates a higher frequency of lambliasis in RAD and shows that family stress was significantly associated with this allergic condition.