1. 50 mg of callus material and settled or filtered suspension cells (fresh weight) respectively are weighed into a 15 ml test tube

2. 300 ml of TTC solution (2 % of TTC in TRIS-HCl buffer 0.05 M, pH 7,5) and 1,2 ml TRIS-HCl buffer (0.05 M, pH 7,5) are added to the cells.

3. The suspension is incubated for 6 hours in the dark.

4. After gentle centrifugation the reaction mixture is removed from the cells.

5. 3 ml of ethanol are added to the cells and the suspension is incubated at room temperature overnight.

6. After gentle centrifugation 2 ml of the cell-free supernatant is pipetted into a glass tube with a screw cap.

7. The extinction of the supernatant is measured at 500 nm

8.1. In case of a new accession: If the E₅₀₀ value is less than 0.05 the cell line is considered to be non viable and the depositor is informed and asked to provide new material (PC/1998/2/3 Appendix 3). If the E₅₀₀ value is between 0,05 and 0,15 the depositor is informed about the low viability and asked to provide new material or more information (PC/1998/2/3 Appendix 2). To check growth the culture is cultivated for 4 weeks in the case of a callus and for 2 weeks in the case of a suspension. If the E₅₀₀ value is higher than 0,15 the culture is considered to be viable and cultivated for 4 weeks in case of a callus culture and 2 weeks case of a suspension culture to check growth.

8.2. In case of a cell line recovered from freeze preservation: A comparison is made either with an actual control culture or with recorded values of a control culture. The viability is expressed as a part of the 100 % viability of the control culture.