A simple technique is described for the preparation of collagen substrata containing 0 1% of collagen by weight, in the form of native bundles with a 640 A period, the substrata are similar in these respects to soft-tissue matrices These substrate are hydrated collagen lattices (HCLs) in which the watery milieu is held within a fibrous collagen net mainly by capillary forces. HCLs have been characterized in terms of the course of collagen precipitation and aggregation, ultrastructure, and their stability under various conditions. The ways in which HCLs can be employed as both two- and three-dimensional substrata in cell behavioral studies are illustrated with some preliminary observations on the form, motility, adhesion, and growth of human diploid cells and two lines of malignant cells.