The cholinergically innervated human eccrine sweat gland is a readily available organ permitting the assessment in allergic patients of cholinergic reactivity with few or no adrenergic influences. The sweat responses of four matched groups (male allergic, female allergic, male control, and female control) to intradermal Mecholyl from 0.1 mug to 100 mug was compared; the 45 male and 45 female allergic patients demonstrated statistically significant increases in sweat responses to essentially all concentrations of Mecholyl examined. No difference in the sweat responses of patients with allergic rhinitis alone was compared with patients with both allergic rhinitis and allergic asthma was noted. Five patients with intrinsic asthma most closely resembled the allergic groups in their responses and 8 patients with vasomotor rhinitis sweated at or below the control groups. The increased sensitivity of allergic patients to cholinergic stimulation as measured by eccrine sweat responses suggest that this hyperresponsiveness may be one of the underlying defects in allergic disease.