INTRODUCTION“Einstecks” refers to a procedure for placing a piece of tissue into the blastocoel of an early gastrula, in order to assess the inductive potential of the introduced tissue. The foreign tissue adheres to surrounding tissue and becomes incorporated into the host embryo. This simple transplant procedure, which is described here, has been used to assess which types of axial tissue can be induced by different regions of the mesendoderm or ectoderm, and how forced expression of genes or treatment with various factors can alter this potential.