Free fatty acids are known for their toxic effects on living cells. The aim of our examinations is the recording of the effect of free fatty acids on the intracellular calcium concentration and the induction of cell death of keratinocytes. It could be shown, that high concentrations of linoleic acid (500-5000 µM) lead within minutes for a distinct rise of the free Ca2+-concentration for a short time. Low concentrations of free fatty acid (e.g. linoleic acid, gamma-linolenic acid and arachidonic acid) led to a continuous increase of the free intracellular [Ca2+]i-content over several minutes. The result that apoptosis occured after adding of fatty acids is probably related to these findings. Annexin-V-FITC and the Cell Death Detection Elisa Test (both Boehringer Mannheim) was used to prove apoptosis. It could be shown, that low concentrations of free fatty acids (linoleic acid up to 50µM, gamma-linolenic acid up to 20µM, arachidonic acid up to 30µM) are tolerated by most keratinocytes, but a minor proportion showed apoptosis too. If a minimal threshold of the concentration is exceeded, the cells are subjected to apoptosis.