The ability of closely related platinum group metal salts (PGMS) to cross-react with the principal sensitising agent ammonium hexachloroplatinate IV was investigated in refinery workers. Selected subjects were screened by skin prick test, specific RAST, RAST inhibition, and primate PCA tests. These showed--but only in platinum-sensitive subjects--a low prevalence of skin and RAST sensitivity to the other PGMS and limited evidence of hapten specific cross-reactivity.