Primary glomerular cells placed in a chemically defined medium containing Waymouth's medium MB 752/1 supplemented with insulin, transferrin, fibroblast growth factor, non-essential amino acids, sodium pyruvate, and antibiotics showed rapid outgrowth of cells which morphologically resembled well differentiated visceral epithelial cells followed by outgrowth of poorly differentiated cells; morphologic evidence suggests these latter cells are precursor cells of the epithelial cell lineage. Whereas the well differentiated glomerular epithelial cells were never observed to divide by sequential phase microscopic observations, a chemically defined medium was developed for optimal growth of the poorly differentiated cell type. This serum-free medium contained Waymouth's medium MB 752/1 supplemented with insulin, transferrin, selenium, and fibronectin (plus non-essential amino acids, sodium pyruvate, and antibiotics). Using this chemically defined medium, we have compared the effects of dimeric and multimeric fibronectin (high molecular weight disulfide-bonded fibronectin produced by incubation of dimeric fibronectin with 3 M guanidine followed by dialysis against 0.05 M cyclohexylaminopropane sulfonic acid (CAPS) buffer, pH 11) on the adhesion and growth of the poorly differentiated primary glomerular cell type. Dimeric fibronectin (FN) was twice as effective as multimeric FN in promoting glomerular cell adhesion, although both forms of FN promoted cell adhesion better than an uncoated substratum. In contrast, cell growth studies demonstrated that multimeric FN was a more potent growth stimulant than dimeric FN. The differential effects of dimeric and multimeric forms of FN in vitro suggests that these molecules may have different functions in vivo. © 1983.