Effect of pectolyase Y-23 and cellulase Onozuka RS on the yield of viable protoplasts of Prunus cerasus L. ""Montmorency"". To isolate leaf mesophyll, leaf and root callus protoplasts of Prunus cerasus L. ""Montmorency"", we have determined the optimum enzymatic mixtures to be used, and characterized the specific activity of these enzymes. The analysis of the specific activities of enzymes allows to compare the different cellulases and pectinases used to obtain protoplasts in relation with the tissue sources. This analysis concerned the FPase (degradation of filter paper) and CMCase activities for cellulases Onozuka RS and R-10, and the PME (pectinmethylesterase), PL (pectate lyase) and PG (polygalacturonase) activities for the pectinases Macerozyme R-10 and Pectolyase Y-23. The results show that the digestion of leaf mesophyll tissues need cellulase Onozuka RS and Pectolyase Y-23 while callus protoplasts of the same material, can be isolated with cellulase Onozuka R-10 and Macerozyme R-10. The enzymes cellulase Onozuka RS and Pectolyase Y-23 (as pectinase) improved significantly the yield and the viability of leaf mesophyll protoplasts compared to cellulase Onozuka R-10 and Macerozyme R-10. These results were correlated to the specific activities of the enzymes. Significant differences between the 2 pectinases are observed for PME, PL and PG activities and between the 2 cellulases for CMCase activity. From callus, the maximum amount of viable protoplasts was obtained with cellulase Onozuka R-10 (low CMCase activity) and Macerozyme R-10 (low PG activity).