1. Arachidonic Acid Metabolism in the Skin -- 2. Arachidonic Acid Metabolism and Tumor Promotion -- 3. Prostaglandins, Epidermal Hyperplasia and Skin Tumor Promotion -- 4. Effects of Phorbol Esters on Phospholipid Metabolism in Vitro -- 5. Tumor Promoting Phorbol Esters May Affect Cell Membrane Signal Transmission by Protein Kinase -- 6. Active Oxygen and Promotion -- 7. Possible Involvement of Arachidonate Products in Tumor Promoter Inhibition of Cell-Cell Communication -- 8. Proteases and Cyclic Nucleotides -- Perspectives