We have transfected an immortalized optic nerve-derived cell line with the cDNA's encoding the two isoforms of MAG. Our aim was to assess whether expression of L-MAG(72 KDa) and S-MAG(67 KDa) in these cells confer adhesion properties when a suspension of single cells is allowed to aggregate. The selected cell lines expressed MAGmRNAs and proteins of the appropriate molecular size, and the proteins were targeted correctly to the plasma membrane. Both L-MAG and S-MAG-expressing transfectants exhibited enhanced self-adhesive properties, aggregating with faster kinetics and forming larger aggregates than MAG-negative control cells. The interaction appears to be mostly heterophilic since MAG⁺ and MAG^-cells which were labeled with a fluorescent probe bound equally well to pre-aggregated MAG⁺ transfectants and their interaction was blocked by monoclonal anti-MAG antibodies. A further finding which supports the role of MAG in adhesion was the observation that MAG was preferentially localized at the junctions between cells, in con fluent cultures.