Summary.— Six cases of allergic reactions to green algae are recorded. Five patients had atopic dermatitis in which exacerbations were provoked both by inhalation and by direct contact with algae. These patients also reacted to lichens, which contain algae in symbiosis with fungi. Five of the patients had allergic rhinitis or asthma, often very mild in relation to the severity of the skin symptoms. Three of the patients also had a delayed hypersensitivity contact dermatitis from lichens, but not from algae.

It is important to investigate patients with suspected sensitivities to lichens and algae both by patch testing and by prick testing as specific desensitization may help those patients with immediate weal reactions.