What is the degree of diligence required of banks in handling deposits?

Extraordinary diligence. The appropriate standard of diligence must be very high, if not the highest, degree of diligence; highest degree of care (PCI Bank vs. CA, 350 SCRA 446, PBCom vs. CA, G.R. No. 121413, 29 Jan. 2001) This applies only to cases where banks are acting in their fiduciary capacity, that is, as depository of the deposits of their depositors. (Reyes v. CA, G.R. No. 118492, Aug. 15, 2001)