In the present study, the ability of a 43 K fragment, originating from the long arm of the 400 K laminin "A" chain (Rao and Kefalides, manuscript in press), to promote the attachment and de novo neurite outgrowth by the pheochromocytoma cell line, (PC12) was studied. Unprimed PC12 cells (not treated with nerve growth factor, NGF), just as the primed cells (treated with NGF), rapidly and efficiently attach to the laminin fragment but less efficiently to the intact laminin coated bacteriological plastic surfaces. The neurite outgrowth was continuous from primed cells attached to both laminin and laminin fragment substrates, when cultured for four days in the presence of NGF. On the other hand, no significant neurite outgrowth was observed from unprimed PC12 cells attached to the laminin fragment coated bacteriological dishes, in the absence of NGF. These data suggest that the 43 K laminin "A" chain fragment contains the PC12 cell attachment promoting site.