The growth and branching patterns of individual identified leech neurons in culture depend upon the molecular composition of the substrate. These differences in morphology have been analyzed quantitatively for nerve cells growing on the plant lectin Con A, on extracellular matrix extract (ECM) containing laminin, and on patterned substrates. The total length of neurite outgrowth was about four times greater, and the number of branching points per unit length was three times smaller on ECM laminin extract than on Con A. Single cells placed on a sharp well-defined border separating Con A and ECM-laminin extract sprouted neurites rapidly on both sides of the border without showing preference for either substrate. An individual nerve cell produced neurites with markedly different structure on the two substrates--curved and thick, with a higher branching frequency on Con A, but straight and slender with a lower branching frequency on ECM-laminin substrate. Similar changes were seen in individual neurites that crossed from one substrate to the other. These results show that local contact of the neuron with a particular substrate induces a particular pattern of local outgrowth. Hence, molecules anchored in extracellular matrix could provide information for regenerating or developing axons regarding the type of branching pattern to be produced in that region.