We studied the relationship of serum immunoglobulin-E (Ig-E) and interleukin-4 (IL-4) concentrations, eosinophil counts, and frequency of respiratory illness with passive smoking in 70 randomly selected children of smoking parents. Fifty randomly selected age-matched children of non-smoking parents served as controls. Children of smoking parents had higher frequency of respiratory illnesses per year (P < 0.01), significantly higher total leucocytic and eosinophil counts, higher percentage of eosinophils (P < 0.01), and higher serum IgE and IL-4 concentrations (P < 0.05) compared to the control group. Serum IgE level was correlated positively with the average number of smoked cigarettes/day, number of siblings, and total leucocytic count. Interleukin-4 concentrations were significantly correlated with the number of smoked cigarettes and IgE levels. Although IgE levels were higher in children of smoking parents (587 +/- 359 IU/ml) compared to controls (189 +/- 21 IU/ml), they did not differ significantly between children with and those without frequent respiratory illness (605 +/- 365 and 557 +/- 354 IU/ml, respectively). Interleukin-4 concentrations were significantly higher in children of smoking parents with frequent respiratory illness (1.8 +/- 0.5 pg/ml) v. those without frequent respiratory illness (1.3 +/- 0.45 pg/ml). Multiple logistic regression analysis revealed that the overall positivity of the risk factors predisposing to respiratory diseases in the study children was 79 percent, and the highest odds ratio was that for IL-4 (OR = 5.15). In conclusion, there is a significant increase in IL-4 and Ig-E concentrations, high eosinophil count and frequent respiratory symptoms in children of smoking parents. It remains that the current state of knowledge on health risks associated with passive smoking warrants that strong preventive action be promoted.