Abstract: A method and apparatus are presented for the casting of gradient gels, without voids, in confined support structures such as thin slab-type configurations. Furthermore, by using a differential activation scheme for the casting, the method makes is possible to produce such gels in slabs of capillary cross-sectional dimension. According to a preferred method, a gradient slab gel is cast by filling a countable number of grooves in a first plate with a first gelling liquid. A gel casting region for a slab gel is formed by spacing the first plate apart from a second plate so as to provide a flow path between the first and second plates which has a directional component orthogonal to the grooves. A second gelling liquid is injected into the gel casting region between the plates, such that the first liquid mixes with the second liquid as the second liquid encounters each groove, thereby forming a gelling mixture with a composition gradient.