We examined the relationship of host factors (age, gender) and environmental determinants (smoking status, area of residence) to indicators of allergy (skin test reactivity and eosinophil count) in a random population sample in the Netherlands. Positive skin test reactivity was associated with age (decreasing with increasing age), with male gender (versus female gender), and with urban residence (versus rural residence). Positive skin test reactivity was not associated with smoking. Elevated eosinophil counts were associated with male gender (versus female gender), with urban residence (versus rural residence), and with current smoking (versus never smoking). Elevated eosinophil counts were not clearly associated with age (if adjusted for the age-related effects of skin test reactivity). Additionally, this study specifically demonstrates that skin test reactivity increases with increasing eosinophil count and vice versa, indicating that the two traits are interrelated. Furthermore, this interrelationship was demonstrated to be age-dependent (decreasing with increasing age).