Abstract: An electrophoresis system which provides enhanced resolution and ability to identify nucleases through use of a two-dimensional technique involving isoelectric focussing of tube gels followed by the electrophoresis of second-dimension slab gels formed by the use of a holder allowing slab gels to be cast directly on the sides of the tube gels. DNA is employed as the enzyme substrate within the slab gels. The slab gels are electrophoresed for the second dimension in a chamber wherein the rack containing a stack of slab gels forms the partition between the anolyte and catholyte compartments. After the second-dimension electrophoresis, the slab gels are incubated in incubation buffer and placed in Pyronin Y to stain the unhydrolized DNA. After staining, they are destained in acetic acid. The DNAses are then visible as colorless spots in a reddish-colored gel.