Abstract
Nerve cells must find correct partner cells during their growth and must form contacts on particular locations on the body or processes of the cell. It is now recognised that cell surface molecules play a decisive part in this recognition through unique molecular surface markers. The immunological approach which has allowed the functional characterisation of specific cell classes, using the cell adhesion molecules L1 and N-CAM, is here described. These molecules show structural similarities localised in a carbohydrate epitope. A new era in developmental neurobiology is forecast.