Minimum eliciting patch test concentrations of cobalt.

In sensitized subjects, minimum eliciting levels of cobalt were estimated using patch tests with aqueous cobalt chloride on both normal skin and on skin pretreated in various ways to enhance penetration and reactivity. 6 reacted to 10,000 ppm and 1 gave an equivocal reaction to 1000 ppm aq. cobalt. Pretreatment of the patch test site for 24 h with surfactant enhanced reactivity, reducing the minimum eliciting concentration to 1000 ppm cobalt chloride in 1 subject, to 100 ppm in 2 subjects, and in 3 subjects to 10 ppm aqueous cobalt chloride. No reactions were obtained at 1 ppm. EDTA was effective in reducing the response to aqueous cobalt.