The factors which determine individual susceptibility to the development of allergic contact dermatitis (ACD) are not well defined. Since it is known that the presence of skin irritation is well-documented as a promoter of sensitization, the sensitivity to irritation of subjects with ACD has been compared with a normal control group. Whilst 78% of those with a positive patch test reaction to the contact allergen colophony (colophonium) responded to a concentration of no higher than 2.5% sodium lauryl sulfate (SLS), only 44% of the matched control group reacted at this level of SLS. Thus, the results are consistent with the hypothesis that individuals with enhanced susceptibility to skin irritation are also more liable to develop allergic skin reactivity.