INTRODUCTIONPreparations of single cells from Xenopus laevis animal caps are useful for assaying the activity of inducing molecules. These dissociated cells can be exposed to more uniform concentrations of inducing factors than the multilayered intact cap. Single cells derived from caps are also used to analyze the role of cell-to-cell contact. This protocol describes the preparation of cells from Xenopus for use in such assays. Animal caps require divalent cations for their integrity and thus can be dissociated by exposure to medium lacking Ca(++) and Mg(++) ions. With this treatment, the cells comprising the inner layers of the cap dissociate within ~20 minutes. Cells can be reaggregated after this treatment and should survive well. The outer layer of cells is more recalcitrant to dissociation and requires a more severe treatment.