In a double blind experimental study, 20 patients with a contact allergy to gold sodium thiosulphate were challenged intramuscularly with the chemically similar gold sodium thiomalate and with placebo. The most spectacular clinical reaction in the 10 patients given the active agent, was an epidermal and dermal flare up of healed patch-test reactions to the gold salts, as well as a high, but transient, rise in body temperature. Previous intradermal tests were similarly reactivated. In addition, toxicoderma-like rashes were observed in several cases, but a flare up of a previous contact dermatitis site was seen in one patient only. The specificity of the positive provocations was demonstrated.