In order to identify organisms with high amounts of the pharmacologically interesting substance scytonemin, dry samples of a cyanobacterial mat (mainly Lyngbya sp. and Anabaena sp.) growing on a rock at the shore near Sao Fransisco do Sul (Brasil) were extracted in 100 % acetone. The supernatant contained high amounts of considerably pure scytonemin (purity about 85 %). After several days to more than 8 weeks in acetone the samples were rehydrated and the photosynthetic activity of the samples was determined by means of pulse amplitue modulated (PAM) fluorescence. Interestingly, the cells showed photosynthestic activity shortly after rehydration. The photosynthetic yield increased within 30 min to about 40 %, which is typical for the unstressed organisms. After extraction and rehydration the cyanobacteria can easily be cultured again. After three weeks of cultivation, the cyanobacteria have again a high concentration of scytonemin in their sheaths. If scytonemin will become a pharmcologically interesting substance, these properties may be used in biotechnology processes for repetitive extraction of a cell culture.