Organotypic cultures can be used for cultivating embryonic kidney rudiments either intact or dissociated into two interacting tissue components. This allows micromanipulations that would hardly be possible in vivo. Especially beneficial is the transfilter technique in which the interacting components are cultured on the opposite sides of a porous filter membrane. This model system allows precise timing of inductive interaction and temporal correlation of various developmental events. On the other hand, the manipulations and the in vitro conditions seem to cause metabolic changes, and long-term cultivation will result in damage to the tissues due to insufficient nutrition. Induced mesenchymal cells cultivated in monolayer cultures behave differently from those in three-dimensional organotypic explants: in the former, differentiation is largely impaired whereas in the latter, development closely resembles that in vivo. Although an organ culture system can never fully mimic embryogenesis in vivo, it offers advantages over cell cultures.