Sensitization and testing of guinea pigs with cobalt chloride

The guinea pig maximization test was used to study the sensitizing potential of cobalt chloride; 1 % CoCl2 was used for injection and 5 % for topical application. The animals were challenged twice; in series I epicutaneous testing was performed 3 weeks after sensitization and intradermal testing after yet another week. In series II the reverse schedule was used, i. e. intradermal testing after 3 weeks and epicutaneous after 4 weeks. CoCl2 was found to be a grade V allergen. The differences between cobalt-exposed and control animals (which had been treated with Freund's adjuvant, petroatum, occlusion, etc.) were statistically significant (P less than 0.001). however, the administration of cobalt at the first challenge testing caused this difference to diminish.